The astronomer Jan Hendrik Oort (1900-1992) left behind an extensive collection of notes and correspondence, both on his research and on matters that concerned him in a variety of official functions. Upon Oort's death, the collection was augmented by more personal papers, letters, journals, and diaries. The resulting collection forms a rich source of information on many aspects of twentieth-century astronomy, in which Oort played such an important role. The scientific and personal material covers the entire span of time from Oort's early youth until his death. To make these papers accessible...