The ATP Challenger Tour is a series of international second-rate men's tennis tournaments, designed and managed by the Association of Tennis Professionals to allow second-rate players to acquire a sufficient ranking to access the main or qualifying draws of tournaments in the ATP Tour.

The first Challenger circuit was born in 1978, with eighteen tournaments during the year. The first two were held in the second week of January, one in Auckland and another in Hobart. Subsequent events took place once a week starting June 18 through August 18 in the United States. The events continued after a month's break. The final event took place in Kyoto. Thirty years later, in 2008, the program offered 178 tournaments located in more than 40 countries around the world.

In 2022, the ATP Tour announced an overhaul of the tournament system and its categories. In 2023 the Challenger 110 and Challenger 90 events have been phased out, the Challenger 80 has been reduced to Challenger 75 and the new top tier, the Challenger 175, has been introduced. The first tournaments in this tier will be played in the second weeks of the Masters 1000 of Indian Wells, Madrid and Rome.

Points are awarded to the winner of the tournament and the losers of the indicated rounds, including the qualifying rounds. A player who qualifies for the main draw receives a bonus of one point which is added to any points he will receive based on subsequent results.