The sequel to Enderís Game and Speaker for the Dead, published in 1991 by Orson Scott Card. Followed by Children of the Mind.After the events of Speaker for the Dead, the human colony on Lusitania has cut ties with Starways Congress and is living openly with the Pequeninos and newly resurrected Formics. Not liking the rebellion and fearing that the deadly Descolada virus native to the planet might get off world, the Congress launches a fleet with the Little Doctor device on it. Ender and his friends have to stop the fleet from bombing Lusitania, eventually, in the next book. Plus other subplots.
Xenocide provides examples of:
Bread, Eggs, Milk, Squick: One of the mentioned methods that the godspoken use to commune with the gods is "checking for accidental murders". This is in a list with "doorway-standing" and "counting multiples of five".
Brother-Sister Incest: Probably nonexistent, but rather maliciously suggested by New Peter, after Ender's soul accidentally creates teenage versions of his siblings from Outside the universe, with New Valentine being inaccurately saintly and beautiful.
This allows Card to issue a Take That toward one of his more obnoxious critics, who decided it was "obvious" that Ender and Valentine were incestuous. Ender replies to the remark above with "God forbid that a brother and sister should love each other!"
Chekhov's Gun: Wang-mu's dream of being the wife and companion of the long-dead Peter the Hegemon.
Decoy Protagonist: The real protagonist of the Path story thread isn't Qing-Jao, it's Wang-Mu.
Deus ex Machina: Outside solves all the major problems of the story, though it causes a few of its own.
Qing-Jao's searches for information discover Demosthenes' identity, i.e. one of the greatest mysteries of the past few millenia, with pretty much no explanation behind it.
Genocide Dilemma: More important now than it was in Enderís Game. It's even in the title, which is a portmanteau of "xeno" (aliens) and "genocide".
Go Mad from the Revelation: Qing Jao goes mad about a quarter of the way through Xenocide and never goes back. Ends up being an Ironic Hell, as she's viewed slowly as the most holy person in all the Hundred Worlds eventually.
I Die Free: After discovering that the descolada virus is not native to Lusitania and may be responsible for pequenino evolution, Planter insists on being placed in the quarantine room where humans are cleansed of the descolada, so he can prove the virus is not what makes piggies sentient. Since his body still needs the descolada to live, though, he suffers the entire time, but dies glad that his mind is truly is own and not that of a parasite.
Idiot Ball: Qing Jao has one superglued to herself, justified because of her devotion to the gods.
Science Marches On: Card did not predict correctly how searches for information would go. Waiting hours for information to turn up simply doesn't happen anymore; the problem is figuring out how to word your queries in such a way to turn up adequate information.
Two-Part Trilogy: Enderís Game began as a stand-alone short story, then was later expanded into a novel. The novel is also sufficiently stand-alone, but the final chapter does have a sequel hook that allows for a sequel if you choose to read it. The sequel also sits surprisingly well as a stand-alone conclusion to Ender's story, but also has a sequel hook if you want to tie up some below-the-surface loose ends. This is where it gets into Two-Part Trilogy country. Xenocide and Children of the Mind, are far more connected than the previous books and were originally intended to be a single volume, but were broken off into two with a superficial cliffhanger between them. Children of the Mind returns to being a suitable conclusion, if you count the main character Ender dying, but only opens up the biggest cliffhanger in literature since Chapterhouse: Dune. Like the Dune series, it's near impossible to differentiate between the overlapping Sequelitis, Two-Part Trilogy, and Trilogy Creep.
What Happened to the Mouse?: Jakt and his trouble in adapting to life on Lusitania get a few mentions early on and then are promptly forgotten.
What Measure Is a Non-Human?: Zig-zagged with the philotic creations. Jane is treated in full accordance with the Hierarchy of Foreignness as raman, a friendly intelligent non-human that can be reasoned with, as are the buggers even after the revelation that Hive Queens are possessed by philotes from Outside rather than actually born intelligent. Yet, the remade Peter and Valentine summoned from Outside by Ender during the FTL test jump are immediately treated as subhuman, inhuman abominations, by virtually all characters, including themselves.
You Should Know This Already: Lusitanian biology is made up of symbiotic plant and animal relationships. Piggies literally become trees, flies pollinate grass, etc.