Einstein on the Beach is an opera in four acts (framed and connected by five "knee plays" or intermezzos), composed by Philip Glass and directed by theatrical producer Robert Wilson. The opera eschews traditional narrative in favor of a formalist approach based on structured spaces laid out by Wilson in a series of storyboards. The music was written "in the spring, summer and fall of 1975." Glass recounts the collaborative process: "I put on the piano and composed each section like a portrait of the drawing before me. The score was begun in the spring of 1975 and completed by the following November, and those drawings were before me all the time." The premiere took place on July 25, 1976, at the Avignon Festival in France. The opera contains writings by Christopher Knowles, Samuel M. Johnson and Lucinda Childs. It is Glass's first and longest opera score, taking approximately five hours in full performance without intermission; given the length, the audience is permitted to enter and leave as desired.

The work became the first in Glass' thematically related Portrait Trilogy, along with Satyagraha (1979), and Akhnaten (1983). These three operas were described by Glass as portraits of people whose personal vision transformed the thinking of their times through the power of ideas rather than by military force.