In celebration of the chart's 55th Anniversary, we're counting down the 100 biggest Hot 100 hits ever.

When Billboard introduced weekly music charts in 1940, there were sales charts and there were airplay charts. These separate charts measuring the popularity of singles continued going their separate ways until Aug. 4, 1958, when Billboard introduced the first chart that blended sales and airplay data. Named the "Hot 100," it has continued to this day, known around the world for being the definitive U.S. singles weekly report. As someone once said, "It ain't No. 1 until it's No. 1 in Billboard."

In celebration of the 55th anniversary of the Hot 100, here is an updated list of the top 100 songs in the tally's history, ranked in order of chart performance -- which we are counting down, 10 per day, until the full list is uncovered. This all-time chart was first compiled for the Hot 100's 50th anniversary; in the five years that have passed, a dozen songs that charted between 2008-2013 have jumped onto the top 100. Come along as we reveal all the songs that made the list.

Scroll to the bottom of this page to read how this list was formulated.