This series contains materials regarding William du Pont's business activities throughout his life. It documents his role in the family explosives businesses beginning at the Repauno Chemical Company in 1880. He served as an officer (such as secretary, treasurer, or president) at Repauno, Hercules Powder Company, The Torpedo Company, E.I. du Pont de Nemours Powder Company, and the Delaware Trust Company. du Pont was a board member for Hinckley Brake Company, Miller Train Control Corporation, Virginia Haloid Company, and Electro Company, and was a major stockholder in the U.S.F. Powder Company and the Vacuum Refrigeration Company.

The amount of materials varies for du Pont's involvement in each company. The U.S.F. Powder Company records document the company's business in its entirety and are a comprehensive source of information on the du Ponts' efforts to create and manufacture flashless powder for the United States Navy, starting in the 1910s through the 1940s. Also well documented is the business of the Repauno Chemical Company, the first du Pont high explosives enterprise in which William du Pont was a close associate of its organizer Lammot du Pont.

Financial documentation of the Montpelier Supply Company depicts the first period of the company's existence, from its incorporation as a Virginia company in 1911 to the death of William du Pont in January 1928; the later documents are included with the papers of William du Pont Jr.

Other companies' materials consist of financial documents and letters to William du Pont from their officers informing him of the state of business, with related enclosures. Additional correspondence with these companies appears in William du Pont's General Correspondence.