#1's is the first compilation album by American singer-songwriter Mariah Carey, released by Columbia Records on November 17, 1998. The album contained Carey's then thirteen number one singles on the Billboard Hot 100, as well as four new songs. In Japan, #1's also included her popular single "All I Want for Christmas Is You", which remained Carey's biggest selling single there. Though showing the characteristics of a regular greatest hits album, Carey expressed a dislike for the track listing, which she called a large collection of her most commercial singles. Carey felt that if #1's was a traditional greatest hits album, then it would include other songs that did not reach number one, but were far more important in her career. She has regularly voiced her frustration with the song choices on the album, expressing her disappointment with the omission of her "favorite songs".

Upon release, reviews for the album were mixed, with criticism directed towards both the new material and the decision to include only Carey's number one hits in the United States. While receiving tepid reviews from music critics, the album became a large commercial success throughout the world. It debuted at number four on Billboard 200, number one in Japan, and in the top-ten throughout almost every major music market around the globe. #1's was certified five-times platinum by the Recording Industry Association of America (RIAA), denoting shipments of five million copies throughout the United States. Aside from the US, the album experienced its strongest sales in Japan, where the album sold 3,250,000 copies in the first three months after its release. The album was certified the triple-million award, and currently remains the best-selling album of all-time in Japan by a non-Asian artist. In Europe, #1's was certified double-platinum by the International Federation of the Phonographic Industry (IFPI), denoting shipments of two million copies throughout the continent.

Three singles were released from the album. Serving as the album's lead single was "Sweetheart" featuring Jermaine Dupri. The song performed weakly on the charts, peaking within the top-twenty only in Germany and Switzerland. The follow-up single, "When You Believe", a duet with Whitney Houston, charted well throughout the world. In the US, the song performed moderately, peaking at number fifteen. In Europe however, the song reached the top-two in Norway, Spain, Sweden and Switzerland and the top-five in Belgium, France, the Netherlands and the United Kingdom. "When You Believe" was featured in the The Prince of Egypt soundtrack, and received the Academy Award for Best Original Song. Sales of #1's were much higher than expected. On May 15, 2015, Carey released #1 to Infinity, an updated version of #1's with all 18 number-ones, which coincides with her residency show in Las Vegas, Mariah Carey Number 1's.