''Three Hearts And Three Lions'' is a fantasy novel by Creator/PoulAnderson published in 1961, expanded from a 1953 novella by Anderson which appeared in Fantasy & Science Fiction.

During UsefulNotes/WorldWarII, Holgar Carlsen is in Denmark, part of LaResistance. Except that at one crucial moment, he finds himself transported to a fantasy world, where the Matter of France from ChivalricRomance, Charlemagne and his paladins, is true. And that he has some sort of connection with this world that he can not remember. He has a pile of armor, and a steed, waiting for him.

A major influence on ''TabletopGame/DungeonsAndDragons''.

Creator/RandallGarrett wrote a pun-filled {{Filk}} version of the novel, with Poul's approval.

!!Tropes found in this work
* AllTrollsAreDifferent: ''Three Hearts and Three Lions'' is, if not the source of the regenerating troll concept, at least one of the earliest known examples.
* AnimatedArmor: Guarding the passes into fairyland.
* BadassBookworm: Holger, in both worlds.
* ChaosIsEvil: The forces of evil are called Chaos; those of good, Order.
* ChickMagnet: Holger, to his surprise. Apparently he never got that lucky back home.
* ChosenOne: Martinus hypothesizes that Holger is this.
* CrushBlush: While dealing with a forward fairy.
* {{Curse}}: Mother Gerd tried one, in the backstory.
* DealWithTheDevil: It's implied that Morgan le Fay has done this, even going so far as to help teach some local barbarians [[DemonLordsAndArchdevils demon worship]], [[HumanSacrifice the Black Mass complete with sacrificing infants]], and [[ImAHumanitarian cannibalism]].
* DemotedMemories: Engineering student Holger Dansk is troubled by odd memories and half-recalled dreams of another place. It takes a near-Death experience when fighting for the Danish Resistance to trigger the truth: he is really the Danish take on King Arthur, recalled to life in a strange otherworld to fight for the soul of his country against alien invasion.
* DoorstopBaby: Holger again. Also Alianora.
* [[FaeriesDonTBelieveInHumansEither Faeries Don't Believe in Humans Either]]: In the fantasy world Holger is transported to, the characters of the Matter of France are historical, but figures like Julius Caesar and Napoleon are legendary.
* TheFairFolk: Complete with the allergy to cold iron and holy names.
* FireKeepsItDead: Holger and friends are fighting a troll, which keeps regenerating until they finally figure out to burn the bits they chop off. This book is the reason it works that way in ''D&D''.
* HumanSacrifice: To a nixie, and in a desecrated church.
* IneptMage: Mother Gerd.
* KillItWithFire: Perhaps the TropeMaker for trolls' vulnerability to fire.
* KnightInShiningArmor: The paladins.
* LeaveYourQuestTest: Morgan Le Fay appeals to him, more than once.
* LoveTriangle: Resolved fairly quickly.
* NiceToTheWaiter: Alianora rescues Hugi.
* TheNoseKnows: Hugi.
* ObliviouslyEvil: The nixie.
* OrderVsChaos: A TropeCodifier.
* OurDwarvesAreAllTheSame: In fact, this ''may'' have been the first work to give dwarves the now iconic [[https://pbs.twimg.com/media/B5Xcf6JCcAAoTU9.jpg thick Scottish accent]]...
* OurSoulsAreDifferent: Not all of us have got them.
* ThePaladin: The paladins of this work are where the original inspiration for the Paladin class from ''TabletopGame/DungeonsAndDragons'' came from.
* RaisedByWolves: Or rather, by dwarves.
* SendMeBack: Holger is suddenly switched out from the climactic battle against evil back to our Earth, where he appears in the middle of a firefight with Nazis. It's ''suggested'' that the battles are connected, and that good triumphed back in the alternate reality, but Holger would like to know for sure.
* ShapeshiftingLover: Alianora.
* SummoningRitual: Mother Gerd says she summoned a sprite.
* SwansASwimming: Alianora is a swanmay.
* TakenForGranite: The Giant.
* {{Unicorn}}: Alianora has one for a while. It finally decamps when Morgan le Fay pays the companions a visit pushing its already sorely tried sensibilities to the breaking point.
* WickedWitch: Mother Gerd.
* YearOutsideHourInside: The elf hill.