EVERYBODY probably recognizes this music - it's the quintessential wedding recessional you've heard at probably a dozen weddings or more. But it has an interesting history.
Mendelssohn wrote this Wedding March in 1842 as part of his suite for Shakespeare's play A Midsummer Night's Dream. But it didn't become popular at actual real-life weddings until after Princess Victoria (daughter of Queen Victoria) chose it for her wedding to Prince Frederick William of Prussia in 1958. The Queen had a fondness for Mendelssohn's music, and Mendelssohn himself often played for her when he visited Britain. And of course as we well know, any time a royal makes a choice for their wedding, it creates all kinds of desire among the "common folk" to imitate it. So this composition has been associated with wedding recessionals ever since then.
Another interesting tidbit about this piece - Vladimir Horowitz, one of the world's most famous concert pianists, arranged the Wedding March as a virtuoso piano piece and played it as the encore at his concerts.
This is typically heard on a pipe organ (probably every organist has it in their repertoire), though I have played it myself on the piano for a wedding recessional. It also can lend a very nice effect to more intimate weddings if done on classical guitar or harp. As you will see in the iTunes excerpts below, it can even be done heavy-metal style!