Dion & the Belmonts were a leading American vocal group of the late 1950s. The group formed when Dion DiMucci joined The Belmonts - Carlo Mastrangelo, Freddie Milano, and Angelo D'Aleo - in late 1957.

After an unsuccessful first single, the group were signed to Laurie Records. Their breakthrough came when "I Wonder Why" made # 22 on the Billboard Hot 100 chart, and the group appeared for the first time on the Dick Clark TV show. They followed it with the ballads "No One Knows" (#19) and "Don't Pity Me" (#40).
This success won Dion and the Belmonts their first major tour in late 1958, with The Coasters, Buddy Holly and Bobby Darin, and this was followed up by the "Winter Dance Party" tour with Holly, Ritchie Valens and The Big Bopper. On 2 February 1959, after playing at Clear Lake, Iowa, Dion decided that he could not afford the $36 cost of a flight to the next venue. The plane crashed, and Holly and the other stars were killed. However, the tour continued, with Jimmy Clanton and Bobby Vee being added to the bill.
In March 1959, Dion and the Belmonts’ next single, "A Teenager in Love", was released, making #5 in the Billboard Hot 100 and #28 in the UK Singles Chart, and this was followed by an album, Presenting Dion and the Belmonts. Their biggest hit, "Where or When", was released in November 1959, and reached #3 on the U.S. chart.
However, in early 1960, Dion checked in to hospital for heroin addiction, a problem he had had since his mid-teens. Further single releases for the group that year were less successful, there were musical and financial disputes between Dion and members of the Belmonts, and in October 1960 Dion decided to quit for a solo career. The Belmonts also continued to release records, but with less success.
Dion and the Belmonts reunited in 1966 for the unsuccessful album Together Again on ABC Records, and again in 1972 for a one-off show at Madison Square Garden, recorded and released as a live album.