1997 saw the debut of the unified worldwide senior tennis circuit. It was an alliance combining the resources of Net Assets, IMG, and the ATP Tour. This unified worldwide circuit was comprised of the ATP Senior Tour of Champions in Europe (which was the successor of the ATP Senior Tour launched in 1992); the Nuveen Tour in North America (which began in 1993); and the Champions Tour on other continents, all sanctioned by the ATP Tour. A total of up to 20 events, featuring great players such as Jimmy Connors, Bjorn Borg, Jose Luis Clerc, Yannick Noah, and Guillermo Vilas, but also John McEnroe, Henri Leconte, Guy Forget, or Mats Wilander, who are still competing on the Champions Tour today.
In 1998, Delta Airlines became the title sponsor of the European tour, which became the Delta Air Lines ATP Senior Tour of Champions. The Nuveen Tour stopped in 1999; and the Success Magazine Tour took over in North America for the 2000-2001 season. That was the time when the Tour format was standardized: as opposed to the 8- or 12-man singles elimination format previously used in the U.S.-based tournaments, the round-robin format used in Europe became and still is the format for the whole Champions Tour.
In 2002, only the Delta Tour of Champions remained in Europe, with a number of events varying from 7 to 11. In 2004, Stanford Financial became the sponsor of the Champions Tour Rankings, a race leading to the London end-of-year event that became the Champions Masters.
The end of 2005 was marked by the termination of the sponsorships of Delta Air Lines and Stanford Financial, opening up the way to a new sponsor and a new title for the ATP Champions Tour in 2006: the Merrill Lynch Tour of Champions.
Matches are contested over the best of three sets, with the deciding set taking the form of a Champions tie-break. The Champions tie-break is an expanded version of the conventional professional tennis tie-break, whereby the winner is the first player to reach 10 points by a margin of 2.
To be eligible to compete on the ATP Champions Tour, players must have been either a World No. 1 during their competitive playing careers, a Grand Slam singles finalist, or a singles player in a victorious Davis Cup team; and they should have retired from the ATP circuit. Each event can also invite two players of its choice to take wild cards.
Players compete for points throughout the year to qualify for The Champions Masters. The Masters takes place at the Royal Albert Hall in London at the end of the year; the player field is comprised of the top ten players in the Champions Tour Rankings after all events, plus two wild cards.
