List of Billboard Hot 100 number ones of 2015
The "Billboard" Hot 100 is a chart that ranks the best-performing singles of the United States. Its data, compiled by Nielsen SoundScan and published by "Billboard" magazine, is based collectively on each single's weekly physical and digital sales, as well as airplay and streaming. During 2015, eight singles reached number one on the Hot 100; a ninth single, "Blank Space" by Taylor Swift, began its run at number one in November 2014. Of those nine number-one singles, three were collaborations. In total, ten acts topped the chart as  either lead or featured artists, with six—Mark Ronson, Charlie Puth, Kendrick Lamar, Omi, The Weeknd and Justin Bieber—achieving their first Hot 100 number-one single. Mark Ronson and Bruno Mars' "Uptown Funk" was the longest-running number-one of the year, leading the chart for fourteen weeks; it subsequently topped the "Billboard" Year-End Hot 100.