"Arthur's Theme (Best That You Can Do)", is a song performed by Christopher Cross, which was the theme to the 1981 film Arthurstarring Dudley Moore and Liza Minnelli. It reached #1 on the US Billboard Hot 100 and in Norway on the VG-lista chart.

The song was written in collaboration between Cross, pop music composer Burt Bacharach, and his frequent writing partner Carole Bayer Sager. A fourth writing credit goes to Minnelli's ex-husband and Australian songwriter Peter Allen, also a frequent collaborator with Bayer Sager; the line "When you get caught between the moon and New York City" from the chorus is taken from an unreleased song they had previously written together.

The song won the 1981 Academy Award for Best Original Song and the Golden Globe Award for Best Original Song. The award was presented by singer Bette Midler, who, in her presentation of the nominated songs, called the song " 'That Song About the Moon and New York City,' also known as 'Four on a Song,' " referring to the four songwriters.

In Japan, the song is known as ニューヨーク・シティ・セレナーデ or "New York City Serenade" and has enjoyed popularity over the years. Cross performed the song with J-pop band SMAP in 2004. The song was even featured in a video that played in Shibuya Crossing (the world's busiest scramble crossing) in 2007.

It is No. 79 on AFI's 100 Years... 100 Songs