Longman premises suffered from two fires, the first in 1861 and the second in the Blitz in December 1940. The archives which remain are therefore not complete, but do form an extensive collection. They are divided into three parts
Part I contains ledgers, registers and bound records relating to the publishing side of the business. They include 'commission' and 'divide' records (referring to items published at the author's expense or with division of profits between author and publisher) 1807-1913; royalty ledgers 1884-1908; statement books 1902-1941; records of dates of publication and of legal deposit 1843-1933; London letter books 1811-1837, 1881, 1914, 1936-1940; Bangkok letter book 1901-1907; Indian letter books 1902-1905, 1929-1945; impression books (recording costs and numbers of copies printed) 1794-1963; copyright ledgers 1794-1926; catalogues of antiquarian books 1814-1846; monthly lists produced for the book trade1858-1917; notes on books published (for the book trade) 1855-1948.
Part II consists of miscellaneous items deemed worthy of preservation by the firm at various points. They include copies booksellers' trade catalogues and lists 1718-1768; correspondence about the discount allowed to booksellers 1894-1898; notebooks and research material of C.J. Longman relating to the publication of House of Longman 1724-1800; selective Longman lists and prospectuses 1802-1901; autograph letters from Longman authors 1799-1900 (authors include Matthew Arnold, Winston Churchill, Edward Bulwer Lytton, Florence Nightingale, Christina Rossetti, Robert Southey, Sir Walter Scott, Charles Dickens, Benjamin Disraeli, William Wordsworth and Thomas Babington Macaulay); scrapbooks of Walter Jefferay, manager of the New York office, 1903-1930s; sundry articles, pamphlets, letters etc. relating to Longman authors 1746-1974; counterpart leases, mortgages and other deeds for Longman properties 1669-1879; papers relating to foreign copyrights 1863-1913; partners' ledgers 1856-1925; staff ledgers 1876-1913; William Longman's letter book 1902-1925 and loose copy-letters 1925-1931; memoranda and certificates relating to share capital 1838-1937; directors' minutes 1931-1948; administrative correspondence files 1930-1970; photographs, prints and drawings of members of the Longman family c. 1800-1962; photographs of Longman staff and premises 1890-1927; letters of condolence on the deaths of Thomas Norton Longman in 1842 and of Thomas Longman IV in 1879;news cuttings and obituaries referring to the Longman family 1877-1896; Longman advertisements and publicity 1916-1967; staff registers 1793-1965; staff memoranda 1862-1901; obituaries and cuttings relating to Longman staff; authors' agreements c. 1800-1959; letters, notes, photographs etc. relating to the history of the Longman family 1662-1972; publishing correspondence 1950-1972.
Contained in both Part I and Part II of the archive are papers relating to firms acquired by Longmans. These include J.W. Parker, Son and Bourne; Sir Richard Phillips; A.J. Valpy; Thomas Cadell.
Part III contains books published by or connected with the firm. These include books with the imprint of precursors of Thomas Longman I at the Sign of the Ship in Paternoster Row; books relating to Longman history; Longman's magazine 1882-1905; selected books with Longman imprints 1725-1970s.