Power pop (also typeset as powerpop) is a form of pop rock based on the early music of bands such as the Who, the Beatles, the Beach Boys, and the Byrds. It originated in the mid-1960s as young music fans began to rebel against the emerging pretensions of rock music and developed mainly among American musicians who came of age during the British Invasion. The genre typically incorporates melodic hooks, vocal harmonies, an energetic performance, and "happy"-sounding music underpinned by a sense of yearning, longing, or despair.