John Sebastian (born March 17, 1944) is an American songwriter and harmonica player. He is best known as a founder of the Lovin' Spoonful, a band named to the Rock and Roll Hall of Fame.

Sebastian was born in Greenwich Village in New York City. His father, also named John Sebastian, was a noted classical harmonica player and his mother was a radio script writer. He grew up surrounded by music and musicians, including Burl Ives and Woody Guthrie and hearing such players as Leadbelly and Mississippi John Hurt in his own neighborhood.

He came up through the Even Dozen Jug Band and the Mugwumps , which split to form the Lovin' Spoonful and the Mamas and Papas. Sebastian was joined by Zal Yanovsky in the Spoonful, which was named after a Mississippi John Hurt song. The band also featured popular drummer-vocalist Joseph Campbell Butler.

The Lovin' Spoonful became part of the American response to the British Invasion and was noted for such folk-flavored hits as "Jug Band Music", "Do You Believe in Magic," "Summer In the City," "Daydream," "Nashville Cats," "Did You Ever have to Make Up Your Mind," "Six O'Clock," and "Younger Girl." The chart-topping band were originally to perform on the television show that became The Monkees and also gained an added bit of publicity when Butler replaced Jim Rado in the role of Claude for a sold-out four-month run with the Broadway production of the rock musical Hair.

In the 1970s, Sebastian had a hit with the theme song to the Welcome Back, Kotter television show, which found new life decades later when a sample from it became the hook for rapper Mase's 2004 hit "Welcome Back". Recently, he has played with John Sebastian and the J-Band, a jug band including Fritz Richmond from the Even Dozen Jug Band, Yank Rachell , an original jug-band leader, and Geoff Muldaur.