The library that John Locke assembled was intended for use rather than for show. Unlike Samuel Pepys, who assembled a collection of some three thousand volumes, about the same size as Locke's, he did not care for display; nor is there evidence to suggest that he, like Pepys, lost sleep over a missing volume. Still, Locke carefully listed his reading and his acquisitions, meticulously keeping a personal catalogue of his books, and arranged for their distribution after his death. About a quarter of his collection remains together at the Bodleian Library, Oxford, the 1978 gift of Paul Mellon.

By the standards of the day Locke's library was sizable, but others were building more impressive collections. John Evelyn's contained about five thousand volumes, and Dr. Thomas Plume, the vicar of Greenwich and archdeacon of Rochester, left some six thousand books at Maldon. On the other hand, Isaac Newton's library contained...