The Left Hand of Darkness 

A book by Ursula K. Le Guin that details the experiences of an ambassador to the frozen world Gethen in an attempt to persuade the planet into joining a United Nations like organization called "The Ekumen of Known Worlds." The book itself is mostly a hypothetical sociological study of a world without gender (as the humans of this world are genderless until they reach a period each month similar to menstruation, where they enter a state called "kemmer" and their bodies switch to either male or female, allowing them to either impregnate someone or to become pregnant) and how Gethen's societies differentiate from other human societies because of this physiological difference.

Guy 1: "You know Le Guin won the Hugo Award for "The Left Hand of Darkness", didn't you?"
Guy 2: "Yeah, but I thought her short story, 'The Ones Who Walked Away from Omelas' was a better example of her writing style."

The Left Hand of Darkness by Roger Whitisissle December 25, 2008