|Men's pro tennis|
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 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.
Challenger tournaments offer total prize money ranging from $30,000 up to $168,000+, which, along with whether the tournament provides hospitality (food and lodging) to the players, determines the number of points a player gets for winning each match in the tournament.
Hospitality moves the points distribution up one level and the points to the overall winner range from 80 points for a $40,000 tournament to 125 points for a $220,000 tournament with hospitality. In contrast, the ATP-level tournaments offer total prize money from $400,000 to over $6 million and points to the overall winners from 250 to 1500.
As a point of reference, player rankings are based on points accumulated in the previous 52 weeks, and as of February 2016, a player who has earned 550 points in the last 52 weeks would be ranked just below the 100th position. 250 points would get him a ranking just below 200th, while with 100 points he would get to around 425th, and 50 points would put him just below 600th. So rankings points earned in Challengers can help a low-ranked player to move up in the rankings quickly.
Points are awarded as follows:
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.
Lu Yen-hsun has won 29 ATP Challenger Tour titles.
Ivo Karlovic became the player who has won a challenger title at the oldest age, winning the 2018 Calgary National Bank Challenger at 39 years, 7 months. 
|Ivo Karlovic||39 years, 7 months||Calgary 2018|
|Dick Norman||38 years, 1 month||Mexico City 2009|
|Stéphane Robert||37 years, 8 months||Burnie 2018|
|Bob Carmichael||37 years, 6 months||Hobart 1978|
|Stéphane Robert||37 years, 5 months||Kobe 2017|
|Víctor Estrella Burgos||37 years||Santo Domingo 2017|