In keeping with Le Guin's soft science fiction style, the setting is used primarily to explore anthropological and sociological ideas. The Ekumen worlds are some dozens of planets populated millions of years ago by human beings from the original human world of Hain. The Hainish used genetic engineering techniques to adapt human beings to non-optimal worlds (for example the androgynes of Gethen in The Left Hand of Darkness).
Hainish civilization subsequently collapsed and the colony planets forgot that other human worlds existed. The Ekumen stories tell of the renewal of interplanetary travel and communication and the efforts to re-establish a galactic "federation".
Especially notable (award-winning) Ekumen novels are The Left Hand of Darkness and The Dispossessed. Other Ekumen novels are Rocannon's World, Planet of Exile, City of Illusions, and The Telling. The series also contains some of Le Guin's short fiction, including the award-winning "The Word for World is Forest" and "The Day Before the Revolution".