O'Neill's own detailed record of his living and writing from 1924 to 1943, the Work Diary, now part of the O'Neill collection at Yale, makes possible the following account of the vast Cycle project: how it was conceived and developed, and how it eventually ended. Although much manuscript material relating to the plays was destroyed, their plots can be reconstructed from scenarios and other notes also preserved at Yale. Outlines of all the plays in the nine-play Cycle are given here in the sequence of their conception as part of the series. They are followed by a summary of the four plays outlined by O'Neill in October and November 1940 to replace plays one and two, actually written between 1935 and 1937, but later destroyed. The four gave the plan its final form - a Cycle of eleven plays.