Piano Phase is a minimalist composition by American composer Steve Reich, written in 1967 for two pianos. It is one of his first attempts at applying his "phasing" technique, which he had previously used in the tape pieces It's Gonna Rain (1965) and Come Out (1966), to live performance.

Stephen Michael Reich is an American composer who is known for his contribution to the development of minimal music in the mid to late 1960s. Reich's work is marked by its use of repetitive figures, slow harmonic rhythm, and canons. 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." For example, his early works experiment with phase shifting, in which one or more repeated phrases plays slower or faster than the others, causing it to go "out of phase." This creates new musical patterns in a perceptible flow.