虽然“前卫”一词隐射了“众中之首”之意，前卫音乐还是给二十世纪后三分之一时期注入了新生。简约主义音乐是在长时间里以一种巡回反复、简单音乐元素的渐变的方式录入的，这在二十世纪60年代有了令人陶醉的开始。简约主义运动的一个最早人物史蒂夫·赖希或许也成为了最受欢迎的人物，他向我们介绍了实验性技巧，允许磁带循环，悄悄倒回到原来的位置。这在作品It’s Gonna Rain(1966)中有体现，它以一个圣·弗朗西斯科街道布道者布道为主题。当来自外界既传统又经典的社交群中的听众开始加入简约主义时，赖希和其他作曲家们开始创作更多的作品。菲利普·格拉斯在二十世纪70年代和80年代的三部曲中与爱因斯坦合作，合作地点有沙滩、Satyagraha和Akhnaten，这巩固了他身为前卫音乐以及流行音乐前沿开拓者的地位。
The modern eras of composition have been friendly to the composer who broke the rules instead of following them. Speaking in general terms, the music of the last hundred years has not been "generic" — that is, it tends not to fall into conventional genres. Composers have written pieces that are sui generis, or one of a kind. The forms, instruments, and ensembles used in music of the twentieth and twenty-first centuries have a dazzling range that in fact is one of avant-garde music's chief attractions for those stimulated by the shock of the new. One notorious composition of the twentieth century, in fact, used no instrumental sound at all: John Cage's 4' 33" simply instructs "any number of players" to sit for that length of time without playing their instruments; the "music" consists of the ambient noise on which the audience is thus induced to focus. While the manifestation is extreme, the spirit of Cage's piece is one that animated many of his contemporaries as they explored the nature of musical sound and shape.
Though it was the questioning spirit of the 1960s that gave full free rein to the avant-garde philosophical imagination, the roots of the movement extend back to the World War I era. The sonic experiments of the Italian futurists inspired a host of efforts to create new instruments and generally to bring new sounds to the musical arena. The 1920s all-percussion works of the Franco-American composer Edgard Varèse still sound well ahead of their time, and new 1920s instruments such as the theremin, the vocal-sounding contraption immortalized in the Beach Boys' "Good Vibrations," forecast an entire tradition of all-electronic compositions later in the century. The ultra-ambitious German composer Karlheinz Stockhausen was one of the earliest and most successful experimenters with electronic sound.
Though the term "avant garde" carries the implication that a work so described is "ahead of the pack," the avant garde gave birth to a genuinely popular movement in the last third of the twentieth century. Minimalist music, which in its pure form featured the reiteration and gradual alteration of single musical ideas over long stretches of time, had its beginnings in the heady 1960s. One of the minimalist movement's earliest figures also became perhaps its most popular: Steve Reich introduced the experimental technique of allowing tape loops to slip slightly out of phase with each other in such works as It's Gonna Rain (1966), which featured a sermon by a San Francisco street preacher. As listeners from outside traditional classical circles began to tune into minimalism, Reich and other composers began to create larger works. Philip Glass's stage trilogy of the late 1970s and 1980s, comprising Einstein on the Beach, Satyagraha, and Akhnaten, cemented his reputation as a composer with avant-garde beginnings and a wide popular reach.