"Aquarius/Let the Sunshine In" (commonly called "The Age of Aquarius" or "Let the Sunshine In") is a medley of two songs written for the 1967 musical Hair by James Rado & Gerome Ragni (lyrics), and Galt MacDermot (music), released as a single by The 5th Dimension. The song peaked at number one for six weeks on the U.S. Billboard Hot 100 pop singles chart in the spring of 1969. The single became the first medley to top the American pop charts and was eventually certified platinum in the U.S. by the RIAA.This song was one of the most popular songs of 1969 worldwide, and in the United States it reached the number one position on both the Billboard Hot 100 (for six weeks in April and May) and the Billboard magazine Adult Contemporaries Chart. It also reached the top of the sales charts in Canada and elsewhere. It was also ranked as the #1 single for 1969.

The recording won both the Grammy Award for Record of the Year and Best Pop Vocal Performance by a Group for the Grammy Awards of 1970, after being published on the album The Age of Aquarius by The 5th Dimension, and also being released as a seven-inch vinyl single record.