40 (song)

"40", also known as "40 (How Long)", is a song by Irish rock band U2. It is the tenth and final track on their 1983 album, War. The song is noted for its live performances; guitarist the Edge and bassist Adam Clayton trade instruments during performances of it, and as it was commonly played to end their concerts, the band would leave the stage one-by-one as the audience continued to sing the refrain "How long to sing this song?". The lyrics are a modification of the Bible's Psalm 40.

The song was released as a commercial single only in Germany, simply to promote U2's appearance at the Loreley Festival in 1983. The single was released on a 7-inch gramophone record with a B-side of the album version of "Two Hearts Beat as One". Since its live debut on 26 February 1983, in Dundee during the War Tour, "40" has been a staple of U2's live concerts, having been performed almost 400 times.