The records of Alex. Brown & Sons span the years 1796-1908, with the bulk of the material dating from 1796 to 1884. Included are business records of successor companies, subsidiaries, and allied business. The records document the commercial and financial activities of Alexander Brown, his sons, and their successors, showing the development of their banking house in conjunction with extensive import-export operations, the building of ships and worldwide trade activities, and the building of the Baltimore & Ohio Railroad. They also reflect the company's change from a mercantile to an international banking house having connections with Brown, Shipley & Company of Liverpool, and with Brown Brothers & Company, of New York, Philadelphia, and Baltimore. The records are organized into the following series: Lettercopy Books, Letterpress Books, Daybooks, Cashbooks, Ledgers, Sterling Ledgers, Ledger Sight Bills, Journals, Sales Books, Waste Books, Accounts Current, Blotters, and Miscellany.

The firm of Alex. Brown & Sons was founded by Alexander Brown, an Irish immigrant who came to Baltimore in 1797 and engaged in the mercantile business as an importer of Irish linen. The records are largely confined to the operations of the firm's outlets in Baltimore, which served as the American headquarters for the firm's chain of offices from 1800 to 1840. Lettercopy and letterpress books generally provide a continuous, daily record of the branch's outgoing correspondence with other offices in the organization and with the branch's out-of-town customers from 1800 to 1879.

Letterbooks, in the collection contain detailed information concerning political, civil, and military affairs affecting the firm. The Lettercopy Books series, consisting of letters sent, includes records of the Falls and Brown Company, 1803-1804. The Letterpress Books series is organized into three subseries. Set A includes records similar to those in the Lettercopy Books series and is distinguished from them chiefly by the copying method. Set B is comprised of letterpress copies of letters sent to Brown Shipley & Company, London, England. The letterpress copies in Set C are of letters sent to Brown Brothers & Company, Boston, New York, and Philadelphia offices.

The collection also includes financial records in a variety of formats. Daybooks are daily journals of business transactions in the order of their occurrence. Cashbooks record money received and paid out, showing date of transaction, name of customer or client, description of the transaction, and amounts received and expended. Ledgers contain postings to accounts receivable and accounts payable; they include ledgers of Falls & Brown, Baltimore, 1796-1810. Sterling Ledgers contain postings to accounts receivable and accounts payable of Alex. Brown & Sons sterling operations. Ledger Sight Bills contain a record of journal postings by bill number. Journals contain daily entries from daybooks and blotters. Sales Books appear to be logs of customer sales. Waste Books are daily journals of business transactions in the order of their occurrence; one book is from Stewart Brown, Philadelphia, and Falls & Brown, Baltimore. Accounts Current appear to be summaries of accounts receivable and accounts payable. Account entries include account name, transaction date, and description. Blotters are daily journals of business transactions.

The Miscellany series includes journals and ledgers of the Union Railroad Company sinking fund, credit rating and statements books, minute books of the Aransas Pass Harbor Company of which Brown and Sons Company was a bondholder and trustee, and of the Female Orphan Asylum, Baltimore. Also in the series is a book containing signatures of persons authorized to conduct business with Brown & Sons Company.

The collection also includes records of other Brown family firms, such as the firms of Stewart Brown, of Philadelphia, an older brother of Alexander Brown, 22 April 1796- 30 May 1797; and of Moore Falls and Stewart Brown of the firm of Falls & Brown, of Baltimore, 1797-1810. These records are not necessarily noted specifically in the descriptions below