Serialism is a technique for composition that uses sets to describe musical elements, and allows the manipulation of those sets. Serialism is often, though not universally, held to begin with twelve-tone technique, which uses a set of the 12 notes of the chromatic scale to form a row (a fixed sequence of the 12 tones of the chromatic scale) as the unifying basis for a composition's melody, harmony, structural progressions, and variations. When not used synonymously, serialism differs from twelve-tone technique in that any number of elements from any musical dimension (called "parameters"), such as duration, register, dynamics, or timbre, and/or pitches, may be ordered in sets of fewer or more than twelve elements. The term "series" should not be confused with the mathematical definition, which nevertheless comes into conjunction when the scales involved are projected from numerical sequences such as the arithmetic series, harmonic series (including its acoustical manifestation as the overtone series and its inversion, the so-called subharmonic series), geometric series, Fibonacci series, or infinity series.

Important serial composers, such as Arnold Schoenberg, Anton Webern, Alban Berg, Karlheinz Stockhausen, Pierre Boulez, Luigi Nono and Jean Barraqué went through extended periods of time in which they disciplined themselves always to use some variety of serialism in writing their music. Other composers such as Béla Bartók, Luciano Berio, Benjamin Britten, Aaron Copland, Olivier Messiaen, Arvo Pärt, Walter Piston, Alfred Schnittke, Dmitri Shostakovich, Igor Stravinsky and even some jazz composers such as Yusef Lateef and Bill Evans used serialism only for some of their compositions or only for some sections of pieces.