The Kalin Twins were an American pop duo, consisting of brothers Hal and Herbie Kalin, who found success in the late 1950s. Known for their harmonic, melancholic ballads, they're best recognized for their hit single "When," which topped UK charts in 1958 and reached number 5 on the U.S. Billboard Hot 100. Their sound, characterized by a blend of rock and roll and pop, was influential during a time when music was transitioning from traditional pop to rock. Despite their brief career, The Kalin Twins contributed significantly to the music of their era.