Free jazz is an approach to jazz music that was first developed in the 1950s and 1960s as musicians attempted to alter, extend, or break down jazz convention, often by discarding fixed chord changes or tempos. Though the music of free jazz composers varied widely, a common feature was dissatisfaction with the limitations of bebop, hard bop, and modal jazz that had developed in the 1940s and 1950s. Often described as avant-garde, free jazz has also been described as an attempt to return jazz to its primitive, often religious, roots and emphasis on collective improvisation.