The "Foundation Trilogy" is a science fiction series written by Isaac Asimov. It consists of three main books: Foundation, Foundation and Empire, and Second Foundation. The story is set in a distant future where a vast Galactic Empire is in decline. A mathematician named Hari Seldon develops a theory called psychohistory, which uses mathematics to predict the future of large populations. Seldon establishes the Foundation, a group of scientists tasked with preserving knowledge and culture to shorten the impending dark age. The trilogy explores themes of power, knowledge, and the cyclical nature of history as various factions vie for control over the galaxy.