The Philosophical Society of Washington is the oldest scientific society in Washington, D.C. It was founded in 1871 by Joseph Henry.
Its aims are "the promotion of science, the advancement of learning, and the free exchange of views among its members on scientific subjects."
Since 1887, the regular meeting place has been the assembly hall of the Cosmos Club, now called the John Wesley Powell auditorium.
Meetings are usually held every other Friday, except in the summer. Meetings are free and open to the public. A lecture is given by a scientist at each meeting. Past speakers have included Fraser Stoddart and Leroy Cronin.