Alfred Lewis Vail, September 25, 1807 – January 18, 1859, was an American machinist and inventor. Along with Samuel Morse, Vail was central in developing and commercializing American telegraphy between 1837 and 1844.

Shortly after Vail graduated from the University of the City of New York in 1836, he met Morse and became interested in Morse’s telegraph experiments. In return for a share in the rights, he agreed to construct telegraph equipment and to bear the cost of obtaining American and foreign patents. Working in Morristown with the financial backing of Vail’s father, Vail, Morse, and a third associate, Leonard D. Gale, made the first successful demonstration of the electric telegraph on January 6, 1838. Public demonstrations followed in New York City and Philadelphia, and in March 1843 Congress authorized construction of a telegraph line between Washington, D.C., and Baltimore, Md. On May 24, 1844, Vail, as Morse’s assistant, received, over the Washington-Baltimore line, the famous first message, “What hath God wrought!” Though Vail continued to work with Morse for another four years, he gradually lost interest in the telegraph and resigned. His cousin Theodore Newton Vail was later the organizer of telephone service in the United States.