The J. Geils Band was an American rock band formed in 1967, in Worcester, Massachusetts, under the leadership of guitarist John "J." Geils. The original band members included vocalist Peter Wolf, harmonica and saxophone player Richard "Magic Dick" Salwitz, drummer Stephen Bladd, vocalist/keyboardist Seth Justman, and bassist Danny Klein. Wolf and Justman served as principal songwriters. The band played R&B-influenced blues rock during the 1970s and soon achieved commercial success before moving toward a more mainstream radio-friendly sound in the early 1980s, which brought the band to its commercial peak. They performed a mix of cover songs of classic blues and R&B songs, along with original compositions written primarily by Wolf and Justman, as well as some group compositions written under the pseudonymous name Juke Joint Jimmy, representing compositions credited to the entire band as a whole. After Wolf left the band in 1983 to pursue a solo career, the band released one more album in 1984 with Justman on lead vocals, before breaking up in 1985. Beginning in 1999, the band had several reunions prior to the death of its namesake, J. Geils, on April 11, 2017.

John Warren Geils Jr., known professionally as J. Geils or Jay Geils, was an American guitarist. He was known as the leader of the J. Geils Band.