交响曲（不等同交响乐）是包含多个乐章的大型管弦乐曲，一般是为管弦乐团创作。

文艺复兴时期就有了交响曲这个说法，当时的交响曲泛指包括了声乐和器乐的一切多声部音乐。

16至17世纪，交响曲用来称呼歌剧和清唱剧中的序曲和间奏曲，这时声乐已经排除在了交响曲的概念以外，“交响曲”从此成为纯粹的器乐曲。

18世纪初，序曲和间奏曲开始脱离歌剧，并开始在音乐会上单独演奏。这对交响曲的发展起重要的作用，意大利那不勒斯的作曲家亚历山大·史卡拉第在自己的作品中为序曲奠定“快板－慢板－快板”（舞曲风格）的三段体式，给后来的交响曲的乐章格式创建了最基本的格式。

A symphony is an extended musical composition in Western classical music, most often written by composers for orchestra. Although the term has had many meanings from its origins in the ancient Greek era, by the late 18th century the word had taken on the meaning common today: a work usually consisting of multiple distinct sections or movements, often four, with the first movement in sonata form. Symphonies are scored for string (violin, viola, cello and double bass), brass, woodwind, and percussion instruments which altogether number about 30–100 musicians. Symphonies are notated in a musical score, which contains all the instrument parts. Orchestral musicians play from parts which contain just the notated music for their instrument. A small number of symphonies also contain vocal parts (e.g., Beethoven's Ninth Symphony).