The following is a list of progressive metal artists, bands and groups. This list contains some bands that at least at some point during their career played progressive metal. Rooted in the early 1980s, the genre fused mellow progressive rock with a heavy metal aesthetic. Characteristics may include complex song structures, unusual time signatures, lengthy songs and often using concept albums. Later on, many extreme metal bands began to experiment and developed an array of progressive metal fusions with other genres, including death metal, black metal, thrash metal and avant-garde metal.