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: