The Left Hand of Darkness by Ursula K. Le Guin

If the female becomes pregnant she remains pregnant through the birth of the child. Some become female and others male and they mate. Every 26 days, in coordination with the moon, they go through a hormonal transformation. The Gethenians have evolved an unusual sexual pattern. While the surface story is interesting and well-written, what makes the book truly unique is its examination of sexuality. The exiled Estraven manages to pose as a guard and free him, and together they travel through the planet's severe cold to try to reach safety.

Genly decides to try to work with one of the other nations on the planet, but there he's arrested and imprisoned by secret police. Genly fails to convince the king to join and Estraven is exiled shortly after.

After two years of proving he is, indeed, an alien and trying to convince the planet to join the coalition he finally is able to arrange a meeting with the king of Karhide, one of the planetary nations, through the help of the prime minister, Estraven. (Le Guin wrote several books set in the 'Hainish' universe.) Genly has been sent as a sole envoy to invite Gethen to join a coalition of around 80 planets called the Ekumen who are united mostly for trade with some loose voluntary laws. This is one of many planets seeded centuries before by a race known as the Hain. In the book Genly Ai travels from earth to an ice-covered planet of humans called Gethen (also called Winter because of its tremendously cold climate). This book, she says, is more of a thought experiment in the tradition of Philip K. Le Guin admits that this type of fiction is often apocalyptic and depressing, perhaps why some people reject reading it. 'What will happen if technology continues to develop in this direction?' it asks. First there's the 'extrapolative', which many if not most readers associate with the genre. In it Le Guin discusses two different types of science fiction. It has been reprinted at least 30 times and luckily the edition I picked up had an introduction by the author. Published in 1969 the book is one of the most influential science fiction books from the last century. Some books you have to go back to once in awhile and Left Hand of Darkness is certainly worth multiple visits.

The Left Hand of Darkness by Ursula K. Le Guin