Urras and Anarres
Urras and Annares form a double planet system (the people of each regard the other as their moon) in orbit around the star Tau Ceti. The Cetians who inhabit both worlds are a very hairy humanoid race which is scientifically advanced.
Urras is divided into many countries with a variety of political systems; Anarres is peopled by the Odonians, an anarchist group in voluntary exile from Urras. The action of The Dispossessed takes place on Urras and Anarres. Urras is also the setting of the short story "The Day Before the Revolution" which appears in the short-story collection The Wind's Twelve Quarters.
Read more about this topic: Terra (Hainish Cycle)