Happy Days made its debut on ABC this day in 1974. It was not an immediate success, and was in fact about to be canceled. At the last minute, a decision was made to try to film the show in front of a live audience instead of using a laugh track. That third season decision proved magical, leading to a decade in prime time. The theme song for the early episodes was "Rock around the Clock" by Bill Haley & the Comets, but eventually the period sitcom got its own theme by Pratt & McLain - a song that became a Top Five hit on the charts. See it and hear it again below.