Chetham's Library began to buy books in August 1655. In the first thirty years the Library bought heavily in theology, law, history, medicine and science. Almost all of the early acquisitions were bought from London booksellers. Most of these books had been published overseas, and many were bought second-hand. The aim was to build up as quickly as possible a collection of books on all subjects which would meet the needs of the clergy, lawyers and medics of Manchester and the surrounding towns.
By the mid-eighteenth century the Library was regarded as a major scholarly collection of books and manuscripts. In terms of acquisitions, there was a shift of emphasis at about that time towards older printed books, large illustrated works and multi-volume periodicals and journals. In 1791 the Library finally published a catalogue of its holdings.
The Library defines its core collection as those works which were acquired from the 1650s up to 1851 when Chetham's ceased to be the main repository for reading matter in Manchester. Until the mid-nineteenth century, Chetham's could claim to be the only true public library in the country. However, following the creation of the rate-supported public libraries, the Library's governors decided that the policy of buying books on all subjects could no longer be sustained and that the Library should concentrate on history and topography.
In the last century this policy was narrowed still further so that the Library now specialises in the history of the north-west of England. Paradoxically, the Library's attempt to reduce the subject scope of its coverage resulted in an increase in the number of books acquired. In the second half of the nineteenth century and beginning of the twentieth the Library gained a large number of additional collections, often by donation.