#1's is the first greatest hits 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, the album also included her popular single, "All I Want for Christmas Is You", which was Carey's biggest selling single there.

The album was met with some criticism regarding the new songs and the decision to only include Carey's number-one hits in the United States. Despite this, the album became a worldwide commercial success. It debuted at number four on the Billboard 200, topped the charts in Japan, Greece, Malaysia and Taiwan; and reached the top-ten throughout almost every major worldwide music market. #1's was certified six-times platinum by the Recording Industry Association of America (RIAA) and double platinum by the International Federation of the Phonographic Industry (IFPI) denoting shipments of five and two million copies. The album reported sales in Japan at 3,250,000 copies in the first three months and remains the best-selling album of all-time in Japan by a non-Asian artist. As of 2021, the album has sold over 15,000,000 units worldwide.

"When You Believe", a duet with Whitney Houston, charted well around the world, peaking at number fifteen in the United States, the top two in Norway, Spain, Sweden and Switzerland and the top five in Belgium, France, the Netherlands and the United Kingdom, and reaching number one in Hungary. "When You Believe" was featured in The Prince of Egypt soundtrack, and received the Academy Award for Best Original Song. The album's third single, "I Still Believe", performed best of the four new songs, peaking at number four.

On May 15, 2015, Carey released #1 to Infinity, an updated version of #1's with 18 of her number ones, to coincide with the beginning of her residency show of the same name in Las Vegas.