Played straight in Adam R. Brown's Alterien series. The children the Alteriens have with humans are half human/Alterien hybrids. Ara, Lyra and Li'nia are also hybrids, though they are half human, half Shanda'ryn.
An early modern version is the boy Jervase Cradock, who is part Fair Folk in The Three Imposters by Arthur Machen.
In Loyal Enemies, humans can have children with elves. Among named characters, Virra the Little Miss Badass and Hraik The Bard are half-elves. Full-blood elves shun them, but humans have nothing against them.
Averted in Poul Anderson's short story, The High Crusade,which includes an instance of the humans finding one or more green-haired, feathery-antennae'd space babes. In the words of the narrator, "Nor was there any possibility of issue between [the Space Babe's] species and our own." Nevertheless, he indicates that the complications didn't stand in the way of Interspecies Romance... though being a priest, he does worry that "the prohibitions of Leviticus might apply," i.e. that it counts as the sin of coupling with beasts.
Piers Anthony's Xanth series, filled with Interspecies Romance (including much Love Potion-induced romance) as it is, has a number of Half Human Hybrids; such hybrids are always fertile, and in some cases entire new races are created this way. It can be taken to ridiculous extents, such as a character who is 1/2 brassy 1/4 human 1/8 ogre and 1/8 nymph.
In cases where the two species involved are otherwise physically... incompatible, love springs have an inherent magic that overrules the laws of biology, allowing for even more bizarre blendings. When the two species are simply too different to coexist in a single form, they become were-creatures, able to transform from the one species to the other.
Hagrid had a human father and a giant mother. Madame Maxime is also at least part-giant, but trying to pass as "pure human."
Fleur Delacour is a quarter Veela.
Marcus Flint is often speculated to have troll-blood in him, though that might just be an insult and not meant to be taken seriously.
Professor Flitwick is "human with a dash of goblin," according to Word of God. Though that's more like "remote goblin ancestor." In the movie it's much more obvious, largely because the same actor plays several of the goblins.
Shadow from American Godswas the son of Odin and a mortal woman. Similarly, Charlie and Spider from Anansi Boys are the sons of the spider god Anansi and a mortal mother.
Tobias from Animorphs. His father was an Andalite (specifically Elfangor) Shapeshifter Mode Locked in human form. While this would seem to make him all human, in the book The Illusion, he is able to see a Genetic Memory of his father, which Andalite legend says can happen when one is near death. This could be a side effect of having acquired Andalite DNA from his uncle, Ax, in the same book.
Marion Zimmer Bradley's The World Wreckers includes a romance and eventually a child between a human and an alien chieri (one of a race of space elves). It's explicit in a number of the books that the Chieri and humans have been interbreeding infrequently for a long time now. In fact, it was the breeding program that created powerful psychics as well as leaving the nobility inbred with a number of "lethal recessives" was brought about to strengthen the psychic gifts inherited from the Chieri. Also, a number of Chieri features show up now and then in the noble families, particularly the ruling Hastur, including abnormally long life, tall slim builds, six fingered hands, and low fertility rates, even compared to the already low norm.
In Patricia Briggs's Hurog novels, half the cast have a dragon ancestor several generations back. (Dragons can assume human form.) There is also Axiel, who is half-dwarf. And his claim to be the dwarf king's son is actually true.
John Carter of Mars, the hero of Edgar Rice Burroughs's A Princess of Mars and subsequent books, had two children with Dejah Thoris, a red Martian princess. Martians lay eggs. Go figure. Then again, John Carter may not be human; he says he is very old and can recall no childhood. There is no mention of the other human/Martian couple in the series (Ulysses Paxton/Valla Dia) having children. The whole thing's made even stranger because it's strongly implied the various Barsoomian Human Aliens can't even fully interbreed with each other; In The Gods Of Mars the White Martians try to expand their gene pool with outbreeding, and get a bunch of pitiful monstrosities that are kept hidden away.
Averted in C. J. Cherryh's Brothers of Earth. A human man is isolated amongst humanoid aliens, but finds a place with them and gets married. Nobody expects the marriage to produce children and it is agreed that he and his wife will try for children for a year and after that the head of the household will step in.
In David Eddings's The Dreamers series, That-Called-the-Vlagh (or just The Vlagh) is a giant female insect who creates thousands and thousands of eggs, and whenever she sees a characteristic she likes, she mixes and matches animals with the characteristics she likes... creating the craziest creatures ever. But very, very, deadly.
Damsel of Austin Grossman's Soon I Will Be Invincible is not the actual child, but the genetic combination of her father's DNA and that of the Green-Skinned Space Babe he fell in love with. This is actually addressed with Damsel confessing that the combination isn't stable and she is constantly sick because of it.
Saaski, the protagonist of the Newbery Medal-winning novel The Moorchild is born among the Folk, which are the traditional Northern European idea of fairies (i.e., pagan spirits of nature fond of music and games, and completely amoral as long as something looks to be fun). However, she is actually the hybrid child of a Folk woman and a human man who wandered into their domain. As she's unable to exercise all the powers of the Folk, and seen as a danger to them, the Prince declares she must be sent out among the humans as a changeling child. Naturally, she doesn't fit in there either, as the humans fear and hate her, and she retains a terror of everyday features of human life like crosses, yellow flowers, salt, and iron (particularly unfortunate as her "adoptive" father is a blacksmith).
In William Hope Hodgson's The Night Land, the Giants are an extremely unpleasant example, "fathered of bestial humans and mothered of monsters." While generally humanoid in form, they're hideous, squat, furry, warty, and bigger than elephants.
In The Three Worlds Cycle books by Ian Irvine there are four humanoid species: Charon, Faellem, Aachim and old human. Those with ancestry from two of the above are blendings, three makes a triune and four makes a tetrach. This may be slightly played with as the books state that many hybrids are sterile, have a short lifespan and various mental and physical problems, these worsening the more "mixed" the blood is.
Also, at least some of these human species are directly derived from others. While it's likely there'd been enough genetic drift to make separate species, it's possible that at least a couple of these races are in fact from the same species. There are other non-human species in the series, but no-one's particularly keen to mate with them to see what happens.
Justified in Dark Lord of Derkholm in which Derk is a magician specialising in genetics and creates griffin children using his and his wife's DNA as well as cat and eagle DNA. However, it is implied that Derk's griffin children will have no problem having children with the "real" griffins that turn up in the second book (well... their Dad can help them out).
In Deep Secret a couple of centaur characters have human fathers. It's pointed out that it has to be that way round because a hybrid foetus would be too big for a human woman to carry.
In House of Many Ways, the insectoid lubbocks reproduce by laying eggs in humans. If the victim is male and doesn't have the eggs surgically removed, he will die, and the resulting offspring is another lubbock. If the victim is female, the victim will usually die in childbirth, and the resulting offspring will be a lubbockin (a Half-Human Hybrid that can interbreed with humans).
The mysterious gualdians of A Sudden Wild Magic. It's not very clear how they're not human, but they consider humans to be a different species and prefer not to interbreed, although it's definitely possible and humans often consider it desirable (to the extent of having very nasty plans for a captured gualdian).
Showed up fairly often in the works of H.P. Lovecraft: The inhabitants of the eponymous town in "The Shadow Over Innsmouth" come to mind in particular, but there were also "The Dunwich Horror," the Jermyn family in "Facts Concerning the Late Arthur Jermyn and His Family" and to a lesser extent, Brown Jenkin in "Dreams in the Witch House." There's a bit of subtext reflecting Lovecraft's famed racist views in how the interbreeding is portrayed as so extremely unnatural.note The problem is not that he presented breeding with a gorilla or a "frog-fish" to be unnatural, the problem is that there was an unspoken component (you know, Subtext) that breeding with a non-white race is also unnatural, because they are no more human than a gorilla.
Author Tract aside, they tend to be pretty grotesque. More notable is Wilbur Whatley in The Dunwich Horror, who, under his roomy clothes, was equal parts giant anthropomorphic goat and and Humanoid Abomination. He wasn't nearly as strange as the Horror, which was a large, invisible monster, when revealed was a mass of tentacles in the shape of an egg, inhuman mouths and eyes everywhere and a humanoid face on top. The twist at the end, if you'll forgive the spoiler, was that Wilbur and the Horror were fraternal twins, with the Horror simply resembling their father Yog Sothoth more than Wilbur did.
Averted entirely in Anne McCaffrey's Freedom's Landing series. There's only one species humanoid enough to be attractive to humans, and it's outright stated that they can't have children together. The children the heroine and her love have are from affairs on her part and a previous marriage on his, both with their own species.
In Un Lun Dun by China Miéville, the character Hemi is half ghost, half human. It's implied that it's extremely rare, and frowned upon by ghosts and humans, for such a pairing to occur.
In Eric Nylund's A Pawn's Dream, all the Dreamers are half (or less) human, as a child born of two Dreamers is incredibly powerful and therefore forbidden, as it would disrupt the balance of power. In this case the intermarrying isn't very far fetched, as the only differences from regular humans are the existence in both worlds and the ability to use magic.
In Tamora Pierce's Wild Magic, Daine Sarrasri is the child of a human woman (Sarra — thus the name) and the god of the hunt (Weiryn). Her mother later becomes a goddess in her own right (The Green Lady). Aly and Nawat's baby from the Trickster books also counts, being half-human and half-crow.
Lampshaded in H. Beam Piper's short story "When in the Course". One human female character is reminded several times throughout the story that, even though the inhabitants of Freya appear human, the two races "started in two different puddles of living slime, seven hundred light-years apart." At the end of the story, she announces that she's pregnant by a Freyan.
Played with in Brian Ruckley's The Godless World Trilogy. The world in question contains 4 sentient species (previously 5, before the werewolf race got wiped out). Of these only two are humanoid, the Huanin (humans) and Kyrinin (elves, but not as long-lived, wise or peaceful as elves tend to be.). The two races can interbreed, but the offspring, called Na'Kyrim, are always sterile and generally conform to real-life hybridization in terms of appearance and shared traits. They also develop a form of magic, known as the "Shared", which given the primary way to become a powerful user of it, tends to cause a great deal of mistrust in the average person. By the way things are looking by the end of the second book, they are very, very justified.
In Christopher Stasheff's Warlock of Gramarye books, Gwendylon Gallowglass of Gramarye is one-quarter elven (and her children are one-eighth). This is weirder than usual, because on Gramarye elves were originally an alien fungus shaped by the beliefs of humans with Psychic Powers.
The most famous Half-Elven family (descending from two separate mixed marriages, whose members married each other) that descended from Lúthien, Beren, and Eärendil. The early members of that family each had to make a choice to be counted among either Elves or Men, because elves and humans have incompatible afterlives for cosmic reasons. Not all members of that family chose the same, causing a lot of grief for them whenever close relatives were separated by the afterlife for all time.
As a further bit, this choice isn't binding on your descendants for the Half-Elven side. In the contemporary setting, the Half-Elven (mostly Elrond and the Rivendell folks) can choose to "opt out" of the Elven immortality and afterlife and instead take the Gift of Man (death). Arwen eventually choose this path to marry Aragorn and eventually dies a mortal death.
The Uruk-hai are implied to be bred by Saruman from orc-human matings.
At least one Man outside the Númenórean royal line mentioned above, Prince Imrahil, has Elven blood.
The half-Elven unions and offsprings mentioned in The Silmarillion and The Lord of the Rings involve (on the elven side) descendants of Elu Thingol, a Sindarin elf and Melian, a Maiar giving them all some Divine Parentage. Early notes on the story indicate that Tolkien originally assumed that being half-elven was not unusual, but no other ever appeared in his work.
In David Weber's Bahzell stories , humans have split into 5 separate species. Humans, Elves, Dwarves, Hradani, and Halfings. It is possible for any of the species to interbreed although only Elf-Human hybrids (Half-Elves) are common—several of the other matches produce offspring that die young or are infertile, although most of the human population of the Axeman Empire have some Dwarf blood. Half-Elves consider themselves to be the fifth species (since they came about before Halflings); however while breeding with each other and with full Elves preserves both the Human and Elvish traits, the offspring of a Human and Half-Elf will show a significant reduction in the Elvish traits. Finally it is established that only Humans and Half-Humans can be wizards or magi.
The Venn family in Obsidian Mirror is rumored to be half-Fae. The truth is a little more complicated. One of Oberon Venn's distant ancestors spent a night in the enchanted woods, where he made a deal with Summer. In exchange for what he was given, one of his descendents would one day choose to enter the Summerland and stay there.
Used early on but mostly averted in the Star Wars Expanded Universe. Two unconnected characters are said to be "hybrids", and it's never explained exactly what species they're hybrids of. Since a lot of different species are related—humanity, for instance, has a long list of "near-humans", offshoots that can in some cases look very unusual—these hybrids might well be more plausible than some of the others on this page. There are also enough mentions of bio-engineering that some species might well be able to make a hybrid. However, in the few examples of Interspecies Romance, it's generally proven true that "the parts match up just fine, but that's about it", as Gavin says of Asyr.
In the X-Wing Series, a minor villain named Zekka Thyne is described as a halfbreed. It's never said what he is besides human, but he's got several Red Right Hands, namely very mottled skin, pointed teeth, and Hellish Pupils that catch the light.
One of the early Star Wars Expanded Universe books has a crossbreed mechanic whose parentage is also never described, who admits to Han Solo that he's not wholly of either species and is relieved when Han is okay with that.
The Star Wars Expanded Universe is filled with hybrids, due to the large number of "Near-Human" races, which aren't so much alien species as subspecies of humanity that descended from early space explorers who were cut off from the original human homeworlds thousands of years earlier, only to be rediscovered later. How far they diverge from regular humans varies; some just have different skin colors, while others have more extreme differences (the Miraluka, for example, have no eyes and see using The Force instead). On the other hand, species that aren't Near-Humans explicitly cannot interbreed with humans, no matter how human-like they appear to be.
Recent additions to the lore rendered near-human argument moot as not only near-humans can interbreed with humans but also species like Zabrak and Twi'lek.
Hybrids ("breeds") are so common in Glen Cook's Garrett, P.I. fantasy series, they sometimes outnumber the human characters. Exempting non-humans from military conscription, then inviting them in to work while your human subjects are off fighting a hundred-year war, can have unintended consequences...
Human/fairy hybrids appear prominently in Goblin Moon and The Gnome's Engine. They are prone to psychological instability and have unique responses to emotional stress, a fact which is central to the plot. A mixed dwarf/human marriage is also mentioned, although it's unstated whether children are expected to follow.
Averted in Neil Gaiman's Stardust, as Tristran and Yvaine get married despite their inability to interbreed.
A straight example would be Tristran himself, as his father was mortal and his mother was a fairy.
The Film of the Book, however, ends with mention of Tristan (different spelling) and Yvaine's children and grandchildren.
In Iain M.Banks The Culture novels, Culture comprises a number of humanoid species who were genetically modified at the Culture's founding to be able to reproduce with each other. Humanoid species from outside the Culture who lack such modifications would not necessarily be able to do the same, sometimes find that the Culture humans look a little unattractive. As masters of genetic tinkering and straight up body re-engineering, there's very little to stop the average Culture citizen from seeking out exciting new alien races as the gender of their choice...
Isaac Asimov's 'Tweenies' short stories features Martian-Human hybrids. There most noticeable features are large white mohican crests and high intelligence. They are outcasts of both species. In the stories a sympathetic human ends up looking after several Tweenies, later becoming a small commune. Once older, they leave Earth to have adventures colonising Venus.
Michael Crichton's Next has Dave, the son of a researcher who manipulated his DNA and a chimpanzee's donated cells. He displays both human and monkey aspects, especially in personality, where he flings poo. It's also implied, that, playing with the theme of genetic engineering gone insane and that people never expect problems with their newfangled tech, he's aging rapidly.
Caspian's tutor, Dr. Cornelius, in Prince Caspian is secretly part dwarf, and it's implied that Caspian's childhood nurse is also descended from dwarfs who'd avoided Telmarine pogroms by passing themselves off as short humans. Caspian's own son is half star, stars being glowing humanoid beings in the world of Narnia. Furthermore, The Magician's Nephew states that the children of Narnia's first human king and queen married wood-nymphs and river-spirits.
In The Magician's Nephew, we also learn that the White Witch—and indeed, all people of Charn—is part giant.
Subverted in Jadis/the White Witch's case, as she only pretended to be part human to assert her claim to the throne. Her non-giant blood is actually genie (jinn), not human.
Vestakia from Mercedes Lackey's The Obsidian Trilogy is, by definition, hellspawn. Around eighteen years before the start of the books, a powerful wildmage discovered she had been seduced and impregnated by a demon who styled himself a Prince of Shadow Mountain. Casting something halfway between a prayer and a spell, she was given a choice between making sure the child would be born looking normal and hoping a mortal upbringing would counter the evil in its soul or making sure the kid's soul was free of demonic taint while dealing with the outward effects of its parentage. She chose option B, confided in her sister, and (with said sister's help) ran.
Also in The Dark Tower series, the Can-Toi, or the "low men" are half-human, half-taheen.
The Half Blood Chronicles by Mercedes Lackey and Andre Norton focus mainly on characters who are the results of elven lords impregnating their human slaves. The half-bloods/wizards are implied to be infertile, though it's never directly stated. The wizards find and save new half-bloods in order to perpetuate themselves as a society; they are never seen to have children of their own loins.
The Dragonlance series of books started the original Chronicles Trilogy off with one of the main characters as a half-elf, the conflicting emotions he felt stemmed from the mixture of his two races and serves as the character's main plot for most of the books; his name Tanis Half-Elven.
Played doubly straight. "Among the Elves... I am Half-Man."
The Bedlam's Bard series by Mercedes Lackey (and varying co-authors) has half-human, half-elven characters, but also states that the species are not cross-fertile unless deliberate actions are taken to make them so. One plotline in one of the books is Beth and Kory searching for a means to accomplish this without resorting to the means used by Perenor to father Ria (Which involved forcibly draining other humans of magic - with frequently lethal consequences).
Humans in Black Dogs seem to be able to hybridize with almost anything, from the plausible elves, Fridge Logic dragons and demons that vary wildly and possess more random body parts in otherworldly dimensions than you can shake a stick at. A couple of these hybrids are even main characters.
Though hybrids have yet to appear prominently in Discworld, it's mentioned a couple of times that humans with dwarf or elf blood exist. Nanny Ogg is the most prominent human character with a trace of dwarf blood, which may explain her short stature and hard-headed ability to survive ballistic farmhouses (not to mention her son Jason's near-supernatural skill at metalwork). It's also mentioned that humans can interbreed with werewolves, with unpredictable results, and at least one major character is a demigod. There is also Susan, Death's granddaughter. While she is only related to Death by adoption, she nonetheless has some of his powers and traits (normal genetic rules apparently do not apply to Anthropomorphic Personifications).
In Kit Whitfield's In Great Waters all the royal houses of Europe (except Switzerland which is landlocked) have Deepman blood. Any hybrid not of royal blood is termed a Bastard and summarily executed, usually by burning. All hybrids have small, needle like teeth, black eyes with no white, clawed and webbed fingers and "legs" that are actually bifurcated tails which force them to use canes to walk. Because of inbreeding royals sometimes exibit other Deepman traits like bioluminescent blue skin (rare even among Deepmen) like Anne or tails that are whole down to the knees like Philip.
"The youth they tortured was like the tall man who came?" he asked at last. "As like as son to father," she answered, and hesitantly: "If the mind could conceive of the offspring of a union of divinity with humanity, it would picture that youth. The gods of old times mated sometimes with mortal women, our legends tell us."
In "The Scarlet Citadel," the alleged Back Story of Tsotha-lanti
In L. Jagi Lamplighter's Prospero's Daughter, Miranda learns that her mother was not who she thought she was, and therefore the demon that addressed a "nephilim" in her presence might have meant her.
The Nephilim of Angelology who are descended from FallenAngels called Watchers. They look like tall, pale and beautiful humans,have lifespans measured in centuries and have wings like their fathers. They also have a warrior caste called Gibborim who are pure white with red eyes but red wings which they can use to create and incendiary wind.
In Jasper Fforde's Something Rotten, the Bradshaws explicitly avert this; they don't have any children because he's a man and she's a gorilla. For double irony — they are fictional characters within the story.
Meredith Gentry, in the series of the same name by Laurell K. Hamilton, is Unseelie Sidhe on her father's side and (I believe) human, brownie, and Seelie Sidhe on her mother's. In fact, about half the cast are hybrids, half-human or otherwise. This is to say nothing of her kids...
The D'Artigo sisters of Yasmine Galenorn's The Otherworld Series have a human mother and a fae father. Additionally, Delilah was born with the powers of a werecat, and Menolly was turned into a vampire. Camille is a Moon Witch, but that's not exactly a species designation. Additionally, it would seem that interbreeding is reasonably common since "ordinary" humans are referred to as FBH's. (Full Blood Humans)
Bruce Coville's book Half Human is a collection of short stories all about this trope. These half-human creatures range from the traditional to the unexpected, with just a few examples being a girl who discovers one morning that her hair has turned into snakes overnight and that her mother doesn't wear a turban all the time just for the Nice Hat factor, another girl who was conceived when her mother drank dragon blood and begins exhibiting dragon-like mannerisms and sprouting ridges on her back when she grows up, and a treetransformed into a man who must learn how to be human.
Also present in Lynn Flewelling's Nightrunner and Tamir series, wherein the Aurënfaie and humans can interbreed, and such interbreeding is the reason some humans possess the ability to use magic. Such mixed-race individuals are known as Ya'shel (they would be half-elves in almost any other universe). This is all made even more interesting by the fact that the Aurënfaie are themselves part-dragon.
There are changelings, who are the scions of humans and one type or another of the Fae. Outwardly, they look human, but as they grow older they take on characteristics of their Fae side; for example, a scion of a human and a troll would become large and brutish and with odd-colored hair. Eventually, the changeling has to "Choose" whether to embrace their faerie heritage and become a full-blooded faerie, or to remain human and lose the faerie powers.
Jared "The Hellhound" Kincaid, a centuries-old hitman who is the scion of a human and something from Down Below.
Thomas Raith, who's the son of the King of the White Court of Vampires and a human wizard called Margaret LeFay Dresden, making him Harry's older half-brother. It's implied that most if not all White Court vampires are the offspring of a human/White mating.
Even Harry's dog Mouse gets in on the action, since he is a Fu Dog, scion of a Tibetan Mastiff and a canine guardian spirit.
In Aleksandr Zarevin's The Lonely Gods of the Universe, many humans are descended from a mix of the original humans and Human Aliens from planet Oll (who pretended to be Greco-Roman gods). Unlike their non-human ancestors, the hybrids are not immortal (the immortality is not due to genetics, though, but due to consuming an alien plant named Ambrosia that gained different properties on Earth). The only thing that appears to be the result of these inter-breedings is humans having different hair colors (apparently, original humans all had dark hair), thanks to the Ollans being redheads.
In The Mortal Instruments, warlocks are the progeny of couplings between humans and demons. They are themselves generally infertile, though Tessa Gray can have children, as her human parent was a Shadowhunter. This was very difficult to arrange, as the runes Shadowhunters bear will kill any warlock children the Shadowhunter might possibly have, but Axel Mortmain eventually arranged to obtain a Shadowhunter without runes.
The shadowhunters or nephilims are also not pure humans, but hybrids of humans and angels. However, they have not been born naturally, but by magic. However, their genes are dominant. If a nephilim with a human have common children, they are also nephilims, even several generations later.
There are also hybrids of fairies and humans, such as the elf-knight Meliorn. A special case Mark and Helen Blackthorn is, because her father was a shadowhunter and her mother was a fairy. Thus, they both are a quarter a human, a quarter an angel, and half a fairy.
Then there's Jonathan Morgenstern. He became a Shadow Hunter, who was also to a large extent a demon, through magical experiments.
In The Dark Artifices it turns out that there are also common offspring of humans and werewolves. The "half-werewolves" can not transform, but they are still significantly stronger, faster and more resistant than humans.
At the same time we see in The Dark Artifices that hybrids between humans and werewolves or fairies, are in no way exceptions, but occur more frequently.
Apparently, a human can produce viable offspring with anything in Jane Gaskell's Atlan series. The invader from the first novel, The Serpent, is the product of a reptile mother and a human father, and later impregnates the heroine, Cija. In the fourth installment, The City, a red ape breeds with Cija, but her mother urges her to abort the resulting fetus.
In The Griffin's Daughter Trilogy, half-human/half-elves - like the title character, Jelena - are known as hikui among the elves, and are treated as second-class citizens, at best. Which is still far better than half-elves are treated in the (human-ruled) Soldaran Empire, where the local religion says elves are demons looking to steal human souls and half-elves are creatures of evil.
John's daughters in Dirge for Prester John: Sefalet (half-blemmye) and Anglitora (half-crane). Anglitora is considered fairly lucky to be a human-looking woman with a crane's wing while Sefalet has no face, instead having eyes and mouths in her hands.
Played straight with Chud', Lyud' and Tat' who can interbreed with humans. The descendants are capable of using the respective Sources of both parents. While Chud' and Lyud' often shun such children, Tat' actively works on both safeguarding their own bloodlines and on raising the amount of human mages by deliberately introducing Chud' and Lyud' genes into the population.
Averted with Moryanas. While a Moryana can bear children with a human, Chud' or Lyud' husband, she will only have daughters who will without exception be Moryanas.
In V. Zykov's Way Home elves are cross-fertile with humans, and half-elves are somewhat bound to elven laws.
Played straight and averted in Katharine Kerr's Deverry series. Dwarves and elves are infertile with each other. However, both races are fertile with humans. And a half-dwarf is shown bearing twin daughters to a father of half-elven heritage.
What really messes with your head is when said half-elf is turned into a dragon... and has a son with another dragon.
Several aspects of the hybridization are played with. There are three half-elf/humans shown in the cast. One is a weak, unstable character and magic/dweomer user, one is a strong dweomer user, and the third is a powerful warrior (but he probably would have been such regardless of his heritage). It is hinted that the human mother of the strong dweomer user may have had some elf-blood in her makeup, as well.
A Thousand Words for Stranger, the first book (publishing-wise) in Julie E. Czerneda's The Clan Chronicles series, mentions rather offhandedly that there are three known species with which humans can have offspring. In all cases, medical intervention is required and the child is infertile. It is implied but never confirmed that the Human Alien protagonist and her human love interest may also be inter-fertile.
In Katherine Kurtz's Deryni works, some characters have one Deryni and one ordinary human parent. The arcane abilities are a dominant trait, so having only one Deryni parent is enough to make an offspring Deryni, and the power isn't additive (in other words, having two Deryni parents doesn't make one more powerful). Sadly, this doesn't prevent Half-Breed Discrimination.
In the J.W. Wells & Co. series, Mr. Tanner, one of the partners, is half-goblin. (His shapeshifting goblin mother works as a receptionist for the firm.)
In The Sky Village, Mei/Dragonfly and Rom/Breaker are tri-human hybrids because they carry the "kaimira gene", which gives them beast (animal), human, and "mek" (robot) DNA.
Paul Richard Corcoran in Mikhail Akhmanov's Retaliation is the son of Lieutenant Abigal McNeil, who was captured by the Faata in the first novel Invasion and impregnated with the genetic material of a high-caste Faata with Psychic Powers. To maintain the secrecy, the child was officially recorded as the son of Abigail McNeil and her lover Lieutenant Richard Corcoran (who was killed aboard the alien ship). Paul grew up to hate his biological father and the entire Faata race. His latent Psychic Powers manifest themselves when he is 37, right when the humans are preparing a strike force to pay the Faata back for the millions of lives lost during the failed Alien Invasion. Strangely, the fleet higher-ups don't consider Paul to be a liability and give him command of a frigate sent with the strike force, figuring his abilities may allow him to infiltrate the enemy. The subsequent books feature Paul's descendants as protagonists, as his genes begin to spread through humanity, and some of them exhibit his Psychic Powers and the "Corcoran curse". One of the descendants, Sergey Valdez, even manages to telepathically sire a child with a Lo'ona Aeo female name Zantu. The resulting child is genetically Lo'ona Aeo, but exhibits some human personality traits, such as desire for adventure and an ability to handle being near aliens (Lo'ona Aeo are xenophobic pacifists).
Akhmanov's Trevelyan's Mission series takes place in the same 'verse but about 500 years after the last Arrivals book. The main character Ivar Trevelyan eventually discovers that he himself is a distant (about 1000 years) descendant of Paul Richard Corcoran, around the time he begins to manifest Psychic Powers and even gains the ability to teleport from world to world.
Averted with the other Human Alien races. The Haptors aren't even sexually compatible with humans. Many other humanoid races aresexually compatible but can't produce offspring together.
Subverted (and deconstructed) by way of Body Horror in Mickey Zucker Reichert and Jennifer Wingert's Spirit Fox. The heroine is a usually-human woman possessed by the spirit of a now-dead fox; she sometimes shapeshifts involuntarily into fox form. During one of these shapeshifted blackouts, she's impregnated by a male fox. She later suffers a miscarriage because her grotesquely malformed half-human, half-fox twin fetuses are not viable.
In Richard Ellis Preston Jr.'s Chronicles Of The Pneumatic Zeppelin, Max and her brother are half human, half "Martian". (The aliens definitely come from much farther away than Mars, but the name stuck.)
Mostly averted in the Riftwar Cycle: humans, elves, dwarves, goblins, dragons, etc. are different species, generally from different worlds. They may be mechanically compatible, but they can't produce offspring. Calis, the offspring of the Queen of the Elves and a half-human, half-Valheru father, is the only exception, and the impossibility of his existence is mentioned from time to time. (His father is pure A Wizard Did It, no breeding involved.)
Vignir, son of Arrow-Odd and the giantess Hildigunn, in The Saga of Arrow-Odd. At ten years, he is already much taller and stronger than his father and also appears much more mature and knowledgeable than one would expect from a human child of that age.
All of the Chimera of The Reynard Cycle are this to one degree or another, though their ability to breed with anything can lead to creatures who are only human in that their great great grandparent had a human head. To keep their kind from completely regressing into animals, many of them kidnap humans for use as unwilling lovers.
Tessa Gray from The Infernal Devices, is a warlock. Her father was a demon who fooled Tessa's mother into thinking he was human.
Myrren Kahliana from Dark Heart is the daughter of a human father and a succubus mother given to him by the priests of Vraxor as a reward for his military service.
Subverted early on in the Mistborn series. There are the nobility and the skaa. While it's fairly obvious to the reader early on that they're all human (or, more technically, a variation of humans tweaked by the Lord Ruler to survive the increasingly Crapsack World) members of both the nobility and the skaa believe that there's an actual difference to varying degrees. The nobility are the ones that have Allomancy (read "magic") and are forbidden to interbreed with the skaa. But, the sheer number of skaa with Allomantic powers (one of the jobs of the Steel Inquisitors is to root out skaa with Allomancy) shows this rule is largely ignored in reality although there are some references to nobles killing skaa after having sex with them to avoid "half breeds."
Although we don't see half-breeds among the other sentient species (the kandra and koloss) it turns out that they're both (mostly) human stock. The koloss are created directly from humans and the kandra are the descendants of humans warped by magic but breed true as non-sentient mistwraiths until given sentience.
One of the protagonists of one of the first science-fiction novels, Auf zwei Planeten ("On Two Planets", 1897) by Kurd Laßwitz, is Friedrich Ell, the son of a Martian explorer stranded on Earth (his spaceship crash-landed in Antarctica) and a German governess living with a family in Australia.
Red Moon Rising has half-vampyres and half-werewulves, as well has vamp/wulf hybrids.
The urban fantasy Red Room series protagonists Derek and Penny Hawthorne are a subversion in that while their mother was a dragon, she was transformed into a human at the time and they are thus completely human. It still makes them subject to Fantastic Racism, though.
In Dragonvarld, Vengeance is roughly human-shaped, but has scaled legs and clawed feet like a dragon, reflecting his father. It nearly gets him killed as a baby, since the midwife raises an angry mob.
Efrel in Kane novel Darkness Weaves has it as her back story. Her mother was raped by ocean-dwelling demons Scylredi and lost her mind. As a result of her mixed blood, Efrel is very skilled at dark arts, not to mention very hard to kill.
Merlin from Amber would qualify, as his father Corwin is (mostly) human, while his mother Dara is a (mostly) shapeshifting demon.
The main, eponymous character and narrator of Seraphina is half-human, half-dragon. Such union is possible, since dragons can take human form - but it is explicitely forbidden by her country's law, not to mention religion. Half-dragons from the book can vary in appearance, from almost-humans with some draconic elements (like a patch of scales somewhere on their bodies) to misshapen monstrosities. And they all share some supernatural powers.
In John Scalzi's The Androids Dream, an attractive pet shop owner turns out to be 18% sheep (specifically, of the Android's Dream variety). Despite this, she looks and acts completely human and doesn't even suspect that she's not 100% human. Her mother was a genetically-engineered Half-Human Hybrid to satisfy the kinds of zoophiliacs. Meanwhile, the followers of the Church of the Evolved Lamb (a self-admitted Scam Religion) see her as the culmination of their prophecies.
Trolls from Malediction Trilogy can breed with humans and produce viable offspring. Mixed bloods usually inherit some magical power of their troll parent but it is greatly reduced. In the troll society, they are invariably slaves and their role depends on their level of magical power.
Inverted in Clive Barker's "Skins of the Fathers", in which it's human males which are the product of hybridization. The Earth's original inhabitants were human women and the many-formed monsters which they took as lovers; the first male human children were the result of crossbreeding experiments Gone Horribly Wrong.
Sebastian Darke is half-human (his father's side) and half-elf (his mother's side). As a result, he has Pointed Ears, causing most people to mistake him for an elf, and him having to awkwardly explain that he's only half-elf.
Theriomorph Chronicles: A Theriomorph is described as a human-animal hybrid that are engineered by Megiddo for minions via genetic engineering, cybernetics and other body modifications, enhancements and augmentations.