Technology
Societies tend to use sophisticated but unobtrusive technologies. Most notable is the ansible, an instant-communication device that keeps worlds in touch with each other.
Physical communication is by NAFAL ships, Nearly As Fast As Light. The physics is never explained: the ship vanishes from where it was and reappears somewhere else many years later. The trip takes slightly longer than it would to cross the same distance at the speed of light, but ship-time is just a few hours for those on board. It cannot apparently be used for trips within a solar system. Trips can begin or end close to a planet, but if used without a "retemporalizer", there are drastic physical effects at the end of long trips. It is also lethal if the traveler is pregnant.
City of Illusions mentions automatic death-machines that work on the ansible principle and can strike instantly at distant worlds. Such a device is clearly used in the events of Rocannon's World. They are not mentioned again in later books.
Churten theory, as developed by the physicists of Anarres, should allow people to go instantly from solar system to solar system. It is a development of the work of Shevek, whose tale is told in The Dispossessed. Shevek's work made the ansible possible - it is mentioned in his tale that engineers decided they could build it once the correct theory was found. Churten theory offers a way to move whole spacecraft instantaneously, but there are side-effects. These are described in two short stories, "The Shobies' Story" and "Dancing to Ganam", both of which appeared in A Fisherman of the Inland Sea.
It should be noted that the ansible has been adopted by several other science fiction and fantasy authors, such as Orson Scott Card, Elizabeth Moon, and Vernor Vinge.
Read more about this topic: Hainish Cycle