What is the name of the first novel in Isaac Asimov's Foundation series?

The first novel in Isaac Asimov’s Foundation series is Foundation. It was published in book form by Gnome Press on August 30, 1951, and began the sequence later known as the Foundation Trilogy.

The book was assembled from interconnected stories and novellas that Asimov originally published in Astounding Science-Fiction between 1942 and 1950. A book-exclusive opening story, “The Psychohistorians,” was added to introduce Hari Seldon and his theory of psychohistory. The novel follows the early stages of Seldon’s plan to preserve human knowledge as the Galactic Empire approaches collapse.

The common mix-up is Prelude to Foundation, which is a prequel written much later and published in 1988. Foundation and Empire followed the original novel in 1952, while Second Foundation completed the initial trilogy in 1953. Although the series later expanded with sequels and prequels, Foundation remains the first published novel in the series.