List of Billboard Adult Contemporary number ones of 2010
Adult Contemporary is a chart published by "Billboard" ranking the top-performing songs in the United States in the adult contemporary music (AC) market. In 2010, eight different songs topped the chart in 52 issues of the magazine, based on weekly airplay data from radio stations compiled by Nielsen Broadcast Data Systems. On the first chart of the year, Taylor Swift was at number one with "You Belong with Me", the song's tenth consecutive week in the top spot. The song's unbroken run at the top ended at 13  weeks, although after two weeks out of the top spot it returned for one further week at number one in the issue of "Billboard" dated February 13. In the early portion of the year three songs had multiple spells at number one, including "Fallin' for You" by Colbie Caillat, which was twice replaced at number one only to rebound to the top of the chart. In the issue of "Billboard" dated April 3, country music group Lady Antebellum began a run of 13 consecutive weeks at number one with "Need You Now". The song was a chart-topper across multiple  genres, and when it spent its tenth week at number one on the AC listing, it broke the record previously held by Rascal Flatts for the longest stay atop that chart by a country act. In topping the AC chart several months after it reached number one on the country listing, the song was seen as part of a trend of country songs quickly gaining success on country radio before going on to impact AC radio at a later date, thereby extending their lifespan across all of "Billboard"s charts. The longest unbroken run at number one in 2010 was achieved  by the band Train's song "Hey, Soul Sister", the group's first chart-topper since 2004, which spent 17 consecutive weeks in the top spot beginning in July. In total the song spent 19 weeks atop the chart in 2010, the most for a single song during the year. It would eventually spend a total of 22 weeks at number one, the second-highest figure at the time for the AC listing behind only Uncle Kracker's version of "Drift Away", which spent 28 weeks in the top spot in 2003 and 2004. Taylor Swift was the only act  with more than one number one during the year, spending five weeks in the top spot with "You Belong with Me" and a single week with "Mine". The former song, which was released in different versions to country and pop/AC radio, has been seen by critics as a key stage in Swift's transition from a country singer to a pop artist. "Mine" was replaced at number one in the issue of "Billboard" dated December 18 by Mariah Carey's "Oh Santa!", which was the final AC number one of 2010. Carey's track had entered the chart the  previous week, meaning that it made the fastest climb to number one since the AC chart began to be compiled using Nielsen data in 1993.