The Bancroft Library is the main special collections library of the University of California, Berkeley. The original collection, acquired in 1905 from its founder Hubert Howe Bancroft, is the largest collection of materials on Californian history and Western North America in the world.

The Bancroft Library's inception dates back to 1859, when William H. Knight, who was then in Bancroft's service as editor of statistical works relative to the Pacific coast, was requested to clear the shelves around Bancroft's desk to receive every book in the store having reference to this country. Looking through his stock he was agreeably surprised to find some 50 or 75 volumes. There was no fixed purpose at this time to collect a library. Noticing accidentally some old pamphlets in an antiquarian book-store, he thought to add these to his nucleus; then looked more attentively through other stores and stalls in San Francisco, Sacramento, Portland and Victoria, purchasing a copy of every book relating to his great and growing subject. During his next visit to the eastern states, without special pains or search, he secured whatever fell under his observation in second-hand stores of New York, Boston and Philadelphia.

He had collected in all not far from a thousand volumes and had begun to feel satisfied. "When, however, (he declares) I visited London and Paris, and rummaged the enormous stocks of second-hand books in the hundreds of stores of that class, my eyes began to open. ... And so it was, when the collection had reached one thousand volumes, I fancied I had them all; when it had grown to 5,000, I saw it was but begun." (177) Finally, special journeys were made to all parts of Europe, as well as the Americas, in the interest of his collection. "And not only was every nook and corner of the world thus ramsacked, but whole libraries were purchased as opportunity offered." While his vague ideas of materials for writing a history gradually assumed more definite form, Bancroft had as yet no idea of writing a history himself. As the collecting proceeded his subject enlarged, until the territory covered was the entire western part of North America from Panama to Alaska, including the Rocky Mountain region, all Central America and Mexico, or about one-twelfth of the earth's entire surface.

The bibliophile reached the settled determination to make his collection as complete as it was possible to make it. Neither time, nor money, nor personal attention would be spared. Agents were appointed in all the leading book marts of the world; no book must be lost because of its high price; no opportunity was to be missed to obtain everything in existence on the subject. By buying up at auction in European cities' individual collections, and even libraries, the Bancroft Library was enriched beyond measure. In 1869, it is reported that Bancroft held, including pamphlets, about 16,000 volumes. These were lodged on the fifth floor of the Market Street building, the original home of the library having been a corner of the second story of the building on Merchant Street.

Bancroft now decided to begin literary work, but the collecting went rapidly forward without interruption. Trembling for the safety of the library through fear of fire, he lent a willing ear to his nephew's proposal to absorb the fifth floor for the purposes of the manufacturing department, of which he had charge. He would erect on some convenient spot a fireproof library building. Among the places considered were Oakland, San Rafael, Sonoma, San Mateo, and Menlo Park; but after a careful canvass and consideration, he selected the well-known site on Valencia Street, near its junction with Mission. The library was moved to the building October 9, 1881. There the library stood for years.

Most of the records of the Spanish and Mexican governments of what is now California (i.e., Las Californias and Alta California) which had been located by American government officials were lost to the fires after the 1906 San Francisco earthquake. Many of those records survive today only because Bancroft himself or his team of researchers made verbatim copies, or took down notes about their contents.

When the question of State purchase was taken up, the Bancroft Library was said to contain from 50,000 to 60,000 volumes of books, pamphlets, maps and manuscripts. Joseph Cummings Rowell, Librarian of the State University, after careful personal examination, estimated the number at 40,000 as a total. For many years, the collection had been offered for sale, Bancroft holding it at US$250,000, which is but a fractional part of the original cost and yet doubtless above the then market price, which Rowell estimated at $140,000, if the complete subject index be included. In 1887, a bill was presented in the State Legislature to purchase the library for the State for $250,000, but the proposition was quickly defeated. Some years later, the University of Chicago considered buying it; naturally there was strong sentiment against permitting the Library to be removed from California and the Pacific States.

In 1905, Reuben Gold Thwaites, Librarian of the State Historical Society of Wisconsin, and one of the foremost book experts in America, was invited to examine the Bancroft Library, "with a view to ascertaining its condition and, so far as may be, its marketable value." In his report, Thwaites characterized the collection of documents, manuscripts, books, pamphlets, and other materials, estimating the total value at upwards of $300,000. The report itself was published November 14, 1905, as a 20-page pamphlet.