Henry Lebbeus Oak (13 May 1844 – 20 May 1905) was an American historian, writer, archivist and librarian.
He was the author of several bestselling books on the history of California and the American west coast.
He was buried in Chapel of Memories Columbarium and Mausoleum, Oakland, Alameda County, California.
He served as the Librarian of the Bancroft Library of San Francisco, California.
After his retirement, he moved to Siegler Springs, California, where he lived out the rest of his life, and wrote about his family genealogical record.