Artists and bands with an extremely long and successful career often have anthology or "essential" collections of their boxes of music released as box sets. These often include rare and never-before-released tracks. Some box sets collect previously released boxes of singles or albums by a music artist, and often collect the complete discography of an artist such as Pink Floyd's Oh, by the Way and Discovery sets. Sometimes bands release expanded versions of their most successful albums such as Pink Floyd's Immersion box set versions of their The Dark Side of the Moon (1973), Wish You Were Here (1975) and The Wall (1979) albums. Pink Floyd have also released The Early Years 1965–1972 box set which features mostly unreleased material.