The Bancroft Library officially dates from 1905, when the University of California acquired Hubert Howe Bancroft's personal library. However, it was actually born 42 years earlier when Bancroft, assisting the editor of a projected guide book to the Western states, discovered 75 volumes pertaining to California and the West on the shelves of his own San Francisco bookstore. Suddenly bitten by the collecting bug, the native New Englander began accumulating works on the history of his adopted state. Over time, the scope of his interests came to encompass the entire Trans-Mississippi West, extending from Alaska to Central America.
Ultimately, Bancroft saw his collection as history awaiting an author. Unable to find scholars willing to tackle his massive accumulation of books and manuscripts, Bancroft elected to write a history himself with the aid of a staff of interviewers, transcribers, and writers. The final work encompassed 39 volumes covering The Native Races, Central America, Mexico, The North Mexican States and Texas, Arizona and New Mexico, California, The Northwest Coast, Alaska, and the remainder of the American West.
Had Bancroft been only a collector and a writer, his contribution to history would have been immense. But because so many of the leading figures in California's history were his contemporaries, Bancroft had the opportunity to accumulate original documents such as the papers of General Mariano Guadelupe Vallejo, and the estate of Sir James Douglas, once governor of British Columbia. Where he was unable to secure original documents, Bancroft had relevant portions transcribed, as in the case of the Archives of Spanish and Mexican California, then in the hands of the U.S. Surveyor General. And where no documents existed, he created them by seeking out and interviewing historical figures. These "Bancroft Dictations" are among the most valuable documents in the collection.
The original scope of the library has enlarged over time to include a number of other special collections such as the former Rare Books Collection. The Bancroft Library now includes the Mark Twain Papers and Project, the Regional Oral History Office, the University of California Archives, the History of Science and Technology Program, and the Pictorial Collection. It has become one of the largest — and busiest — special collections in the United States.