Mendelssohn's Wedding March was one of the first pieces he wrote for A Midsummer Night's Dream, from before he undertook to compose a complete incidental score for the play.
Structurally, it is a rondo: the recurring theme (the "bread" of the "rondo sandwich") is a brief fanfare, leading into a march tune, which at times alternates with a secondary melody. The first "episode" is a second march tune, while the second is a short bridge leading into a trio.
At weddings in many English-speaking countries, this piece is commonly used as a recessional, though frequently stripped of its episodes in this context