Reich's work is marked by its use of repetitive figures, slow harmonic rhythm, and canons. His compositional style reflects his explicit rejection of Western classical traditions, serialism, and indeterminacy, because, unlike these traditions, he sought to create music in which the compositional process was discernible in the music itself. Reich describes this concept in his essay, “Music as a Gradual Process,” by stating, “I am interested in perceptible processes. I want to be able to hear the process happening throughout the sounding music.” To do so, his music employs the technique of phase shifting, in which a phrase is slightly altered over time, in a flow that is clearly perceptible to the listener. His innovations include using tape loops to create phasing patterns, as on the early compositions It's Gonna Rain (1965) and Come Out (1966), and the use of simple, audible processes, as on Pendulum Music (1968) and Four Organs (1970). The 1978 recording Music for 18 Musicians would help entrench minimalism as a movement. Reich's work took on a darker character in the 1980s with the introduction of historical themes as well as themes from his Jewish heritage, notably Different Trains (1988).
Reich's style of composition has influenced many contemporary composers and groups, especially in the US. Writing in The Guardian, music critic Andrew Clements suggested that Reich is one of "a handful of living composers who can legitimately claim to have altered the direction of musical history".