William Sebastian Cohen (born 28 August 1940) is an author and American politician from the U.S. state of Maine. A Republican, Cohen served as Secretary of Defense (1997–2001) under Democratic President Bill Clinton.

Cohen was born in Bangor, Maine. His father, Reuben Cohen, was a Russian-Jewish immigrant and life long baker (Bangor Rye Company). His mother, Clara, was of Irish-Protestant ancestry.

After graduating from Bangor High School in 1958, Cohen attended Bowdoin College, graduating cum laude with a Bachelor of Arts degree in Latin in 1962.