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 top tier of men's tennis is the ATP World Tour, Challenger Tour events are the second highest level of competition, and the Futures tournaments on the ITF Men's Circuit are the third and final tier of international professional 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 World Tour tournaments.

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.

Adrian Ungur (born January 25, 1985) is a Romanian tennis player playing on the ATP Challenger Tour and member of the Romania Davis Cup Team. On May 21, 2012, he reached his highest ATP singles ranking of 91. He is coached by Fabrizio Fanucci. His most notable result was a four set victory over David Nalbandian in the first round of the 2012 French Open.

In 2006 Adrian married Liana, who is also a professional tennis player and daughter of Romanian football legend Ilie Balaci.

Following some good results in Challenger events, Adrian was entered into the main draw at the French Open, his first main draw appearance at Grand Slam level. He beat former world number three David Nalbandian in the first round, before being defeated in four sets by Roger Federer in the second round - although he saved two match points in winning the third set.

Filippo Volandri (born on 5 September 1981 in Livorno, Italy) is an Italian professional male tennis player. Volandri is a right-handed player who reached a career-high ranking of 25 on July 23, 2007. He turned pro in 1997, and as of January 2006, had earned over $1,300,000 in prize money. In September 2006, he lost the final of the Bucharest ATP tournament against Jürgen Melzer 6–1, 7–5. Volandri won the second title of his career in September 2006, beating Nicolás Lapentti in the final of the Sicily International in Palermo.

At the Rome Masters in 2007 Volandri, having entered as a wild card, recorded the biggest win of his career by dispatching world number one Roger Federer in straight sets 6–2, 6–4. Volandri celebrated by doing a lap of honour around centre court, high-fiving spectators in the furthest-forward rows.^{[citation needed]}

Afterwards Volandri hailed the victory as not only for himself but for Italy, telling something of the regard in which Federer, who holds the record for the longest spell as the world's top-ranked male player, is held.^{[citation needed]} The result was all the more felt due to Italy's relative under-achievement on the men's tennis scene in recent times.^{[citation needed]} For his part Federer offered few excuses for the out-of-character display.^{[citation needed]}

Nicolás Alejandro Massú Fried (born October 10, 1979, in Viña del Mar, Chile), nicknamed Vampiro (Spanish: "vampire"), is a Chilean tennis player, a former World No. 9 in singles, and a two-time Olympic gold medalist. He is the only male player to have won both the singles and doubles gold medals in the same Olympic Games in modern (1988 ff.) Olympic tennis.

Massú was introduced to tennis at age five by his Hungarian grandfather, Ladislao Fried. From age 12, he was trained at the Valle Dorado tennis academy, near Villa Alemana, by Leonardo Zuleta, with whom he perfected his forehand and double-handed backhand. He later trained at the Nick Bollettieri academy, in Florida, United States, alongside Marcelo Ríos, and later at the High Performance Center in Barcelona, Spain.

Massú became a professional tennis player in 1997. That year he won the prestigious juniors year-end Orange Bowl tournament. He also claimed the boys doubles competitions at Wimbledon (with Peru's Luis Horna) and the US Open (with countryman Fernando González), and was junior doubles world champion.

Hiroki Kondo (近藤 大生^?) (born 5 November 1982 in Aichi, Japan) is a Japanese tennis player. On April 12, 2010, he reached his highest ATP Doubles ranking of 179.