The ATP Challenger Tour, known until the end of 2008 as the ATP Challenger Series, is a series of international men's professional tennis tournaments. The Challenger Tour events are the second-highest tier of tennis competition, behind the ATP Tour. The ITF World Tennis Tour tournaments are on the entry-level of international professional tennis competition. The ATP Challenger Tour is administered by the Association of Tennis Professionals. Players who succeed on the ATP Challenger Tour earn sufficient ranking points to become eligible for main draw or qualifying draw entry at ATP Tour tournaments. Players on the Challenger Tour are usually young players looking to advance their careers, those who fail to qualify for ATP events, or former ATP players looking to get back into the big tour.

The first challenger events were held in 1978, with eighteen events taking place. Two were held on the week beginning January 8, one in Auckland and another in Hobart. The next events were held one at a time beginning June 18 and ending August 18 in the following U.S. locations, in order: Shreveport, Birmingham, Asheville, Raleigh, Hilton Head, Virginia Beach, Wall, Cape Cod, and Lancaster. Events continued after a one-month hiatus with two begun September 24 and 25, one in Tinton Falls, New Jersey and in Lincoln, Nebraska respectively. The following week saw one event played, in Salt Lake City, then two played simultaneously in Tel Aviv and San Ramon, California, then one played the following week in Pasadena. A final event was played a month later in Kyoto. In comparison, the 2008 schedule saw 178 events played in more than 40 countries.

In efforts to further the progression of college and junior players into the professional tour, the ATP Challenger Tour has partnered with the Intercollegiate Tennis Association (ITA) and the International Tennis Federation (ITF) to give players more opportunities on the professional tour. Those that finish in the top 10 of the end-of-year college rankings are now eligible for six wild cards into the main draw of Challenger events, and if they have finished their college education, they receive 8 of those wild cards. Those that finish in the 11 through 20 range of the collegiate rankings are eligible for six qualifying wild cards, with those who have completed their college education being eligible for eight wild cards.^[1]

Much like the partnership with the ITA, the Challenger Tour also partnered with the ITF. This partnership granted those with year-end rankings inside the top 10 in the world eligible for eight main draw Challenger Tour wildcards, and those who finished the year between 11 and 20 in the world receiving eight Challenger Tour qualifying wildcards.^[2]

Players have usually had success at the Futures tournaments of the ITF Men's Circuit before competing in Challengers. Due to the lower level of points and money available at the Challenger level, most players in a Challenger have a world ranking of 100 to 500 for a $35K tournament and 50 to 250 for a $150K tournament. An exception happens during the second week of a Grand Slam tournament, when top-100 players who have already lost in the Slam try to take a wild card entry into a Challenger tournament beginning that second week.

In February 2007, Tretorn became the official ball of the Challenger Series, and the sponsor of a new series consisting of those Challenger tournaments with prize money of $100,000 or more. They renewed the sponsorship with the ATP in 2010 and extended it until the end of 2011.

The Tampere Open is the longest running ATP Challenger event.^[3]

• 2024 ATP Challenger Tour
• ATP Tour
• ITF Men's World Tennis Tour
• WTA 125 tournaments