The Bubbling Under Hot 100 Singles is a chart published weekly by Billboard magazine in the United States. The chart lists the top 25 songs below number 100 that have not yet charted on the Billboard Hot 100. Chart rankings are based on radio airplay and sales.

Initially, the chart listed 15 positions, but expanded to as many as 35 during the 1960s, particularly during years when over 1,000 singles made the Billboard Hot 100 chart. From 1974 to 1985, the chart consisted of 10 positions. Since 1992, the Bubbling Under Hot 100 Singles chart has listed 25 positions.

The chart was introduced in the June 1, 1959 issue of Billboard under the name "Bubbling Under the Hot 100". Containing a listing of 15 singles, the chart was described as a "new listing that predicts which new records will become chart climbers." Its first number-one single was "A Prayer and a Juke Box" by Little Anthony and the Imperials.

It would continue to be published in Billboard until the August 24, 1985 issue, after which it was discontinued. Prior to its discontinuation, the chart had not been issued in four issues; three from 1974 and one in 1978. However, it quietly re-appeared in the December 5, 1992 issue of Billboard and continues to the present day.

The Billboard Hot 100 is the United States music industry standard singles popularity chart issued weekly by Billboard magazine. Chart rankings are based on radio play and sales; the tracking-week for sales begins on Monday and ends on Sunday, while the radio play tracking-week runs from Wednesday to Tuesday. A new chart is compiled and officially released to the public by Billboard on Thursday. Each chart is dated with the "week-ending" date of the Saturday two weeks after. Example:

The first number one song of the Hot 100 was "Poor Little Fool" by Ricky Nelson on August 4, 1958. As of the issue for the week ending June 9, 2012, the Hot 100 has had 1,015 different number-one hits. Its current number-one is "Somebody That I Used to Know" by Gotye featuring Kimbra.

What has always been known as the Hot 100 had existed for nearly fifteen years as numerous charts, tracking and ranking the most popular singles of the day in several areas. During the 1940s and 1950s, popular singles were ranked in three significant charts: