Sondheim wrote the song specifically for the actress Glynis Johns, who created the role of Desirée on Broadway. The song is structured with four verses and a bridge, and uses a complex compound meter. It became Sondheim's most popular song after Frank Sinatra recorded it in 1973 and Judy Collins' version charted in 1975 and 1977. Subsequently, Sarah Vaughan, Judi Dench, Grace Jones, Barbra Streisand, Shirley Bassey, Zarah Leander, Tiger Lillies, Ray Conniff, Glenn Close, Cher and many other artists recorded the song and it became a jazz standard.

The "clowns" in the title do not refer to circus clowns. Instead, they symbolize fools, as Sondheim explained in a 1990 interview:

I get a lot of letters over the years asking what the title means and what the song's about; I never thought it would be in any way esoteric. I wanted to use theatrical imagery in the song, because she's an actress, but it's not supposed to be a circus [...] [I]t's a theater reference meaning "if the show isn't going well, let's send in the clowns"; in other words, "let's do the jokes." I always want to know, when I'm writing a song, what the end is going to be, so "Send in the Clowns" didn't settle in until I got the notion, "Don't bother, they're here", which means that "We are the fools."^[1]

In a 2008 interview, Sondheim further clarified:

As I think of it now, the song could have been called "Send in the Fools". I knew I was writing a song in which Desirée is saying, "aren't we foolish" or "aren't we fools?" Well, a synonym for fools is clowns, but "Send in the Fools" doesn't have the same ring to it...^[2]