The Isley Brothers () are an American musical group originally from Cincinnati, Ohio, that started as a vocal trio consisting of brothers O'Kelly Isley Jr., Rudolph Isley and Ronald Isley in the 1950s. With a career spanning over seven decades, the group has enjoyed one of the "longest, most influential, and most diverse careers in the pantheon of popular music".

Together with a fourth brother, Vernon, the group performed gospel music until Vernon's death a few years after its formation. After moving to the New York City area in the late 1950s, the group had their first successes during these early years, first coming to prominence in 1959 with their fourth single, "Shout", written by the three brothers. Initially a modest charted single, the song eventually sold over a million copies. In the 1960s, the group recorded songs for a variety of labels, including the top 20 single "Twist and Shout" and the Motown single "This Old Heart of Mine (Is Weak for You)", before recording and issuing the Grammy Award-winning hit "It's Your Thing" on their own label, T-Neck Records.

Influenced by gospel and doo-wop music, the group began experimenting with different musical styles incorporating elements of rock and funk as well as pop balladry. The inclusion of younger brothers Ernie Isley (lead guitar, drums) and Marvin Isley (bass guitar), and Rudolph's brother-in-law Chris Jasper (keyboards, synthesizers), in 1973 turned the original vocal trio into a complete band and reached the height of their success. For the next full decade, they recorded a string of top-selling albums from 3 + 3 to Between the Sheets, including the number one album The Heat Is On.

The six-member band splintered in 1983, with Ernie, Marvin, and Chris Jasper forming the short-lived spinoff group Isley-Jasper-Isley. The oldest member, O'Kelly, died in 1986 and Rudolph and Ronald released a pair of albums as a duo before Rudolph retired to a life in the Christian ministry in 1989. Ronald reconvened the group two years later in 1991 with Ernie and Marvin; five years later, in 1996, Marvin Isley left the group due to complications of diabetes. The remaining duo of Ronald and Ernie achieved mainstream success with the albums Mission to Please (1996), Eternal (2001) and Body Kiss (2003). Eternal spawned the top twenty hit "Contagious". As of 2019, the Isley Brothers continue to perform under the lineup of Ronald and Ernie.

The Isley Brothers have sold over 18 million units in the United States alone. They have had several hit songs including four Top 10 singles on the United States Billboard chart. With their first major hit charting in 1959 ("Shout"), and their last one in 2001 ("Contagious"), they are among the few groups ever to have hit the Billboard Hot 100 with new music in five different decades. Sixteen of their albums charted in the Top 40 and thirteen of those albums have been certified gold, platinum or multi-platinum by the RIAA. The brothers have been honored by several musical institutions, including the Rock and Roll Hall of Fame, which inducted them in 1992. Five years later, they were added to Hollywood's Rockwalk, and in 2003 they were inducted to the Vocal Group Hall of Fame. They received the Grammy Lifetime Achievement Award in 2014.