A genius (Hari Seldon) develops a scientific method to predict the future, and in so doing foresees the fall of the then-dominant Empire and an ensuing Dark Age. Before his death, Seldon uses these new methods to develop an ultra long-range plan to shorten the Dark Age to a mere 10,000 years, beginning with the establishment of a scientific colony (the Foundation) at the edge of the galaxy.
Soon after Seldon's death, the Foundation project begins to evolve in response to a series of crises that Seldon has foreseen.
(See the Wikipedia page for a more detailed overview )