The Birthday of the World: and Other Stories is a collection of short fiction by Ursula K. Le Guin, and first published in March, 2002 by HarperCollins. All of the stories except "Paradises Lost" were previously published individually elsewhere.
A young Karhidian loses "her" virginity during "her" first phase of coming into heat, called a "kemmer". The gender is in quotations because most Gethenians only become female or male during kemmer and then return to their neutral/hermaphroditic state.
"The Matter of Seggri" - Spring 1994 in Crank!. Takes place on Seggri of the Ekumen.
The discovery, exploration, and ultimate alteration of a planet characterised by extreme gender imbalance and segregation.
"Unchosen Love" - Fall 1994 in Amazing Stories. Takes place on O of the Ekumen which is the same planet as the title story of A Fisherman of the Inland Sea. Society there is built around the sedoretu - a marriage involving four people.
About a meek man and meek woman, who are in relationships with strong-willed man and woman respectively. The meek find solace in each other's company, an unexpected relationship catalyzed by mysterious encounters.
"Mountain Ways" - August 1996 in Asimov's Science Fiction. Also on O.
Two women who are in love, but who cannot find suitable partners to establish a sedoretu, decide to deceive the other parties to a marriage by disguising one of the women as a man. Complex and beautiful story.
"Solitude" - December 1994 in The Magazine of Fantasy and Science Fiction. Takes place on Eleven-Soro on the fringes of the Ekumen. Society has fragmented - men and women live apart, and adult women do not even enter each other's houses. The story is told by the daughter of a mobile of the Ekumen who grows up in this society.
"Old Music and the Slave Women" - 1999 in Far Horizons ed. R. Silverberg. Another story in the same dual-planet system of Werel and Yeowe as Four Ways to Forgiveness of the Ekumen. It is set later in time than the stories in that volume, when the "assets" of Voe Deo on Werel are fighting a war to gain freedom from the "owners".
"The Birthday of the World" - June 2000 in The Magazine of Fantasy and Science Fiction. May or may not be of the Ekumen. The story depicts a society where the hereditary rulers are "God" - and how the society is disrupted from inside and outside. The situation has parallels to that of European contact with the Inca.
"Paradises Lost" - First publication. Not of the Ekumen. A story of a group of humans undertaking a journey to a distant planet to discover the possibilities of habitability. The journey takes several generations, and is told from the perspective of people that have grown up aboard the ship and its unique society.