Aside from Elton's own catalog of recordings, he's also contributed to other artists' projects, and recorded songs for dozens of compilations, soundtracks and tributes. Many of them feature Elton on lead or shared vocals, but some are backing vocals or piano only. The majority of these side projects were released on full-length albums, with a few issued only as singles. In most cases, these records are the only source for the songs, though some contain exclusively live or alternate recordings of Elton's hits.