The Champions Series was a series of tennis tournaments designed for former champion members of the ATP Tour. It operated from 2006 to 2021.
It consisted of tournaments where top players of the sport competed in one-night, four-player events with two one-set semifinal matches and a one-set championship match played in one evening. Eligible players competing on the Champions Series either held a Top 5 singles ranking; been a Grand-Slam singles finalist, or a singles player on a championship Davis Cup team during their ATP tour playing careers. It also allowed one wild card of their choice at each event. The series was produced by Inside Out Sports & Entertainment. The minimum age to participate in a tournament was 30.
No matches were played in 2013 as the series realigned from the fall to the spring. A new match format was introduced to complete all play on a single evening, with only four players involved. The new format is two semi-final matches consisting of a best-of-one-tiebreak set, followed by a one-set final for the championship.
In 2006, Outback Steakhouse became the first sponsor with naming rights of the series.
In October 2011, Invesco QQQ signed a multi-year agreement to become the title sponsor.
Top ranked players included:
The Oliver Group Champions Cup, March 12–16, 2008
The Residences at the Ritz-Carlton, Grand Cayman Legends Championship, April 16–20, 2008
Champions Cup Boston, April 30- May 4, 2008
The Oliver Group Champions Cup, March 7–11, 2007
Champions Cup Boston, May 2–6, 2007
Champions Cup Athens, May 17–20, 2007
The Gibson Guitar Champions Cup, August 22–26, 2007
The Championships at the Palisades, September 26–30, 2007
The Stanford Championships, October 18–21, 2007
The Legends Rock Dubai, November 20–24, 2007
Champions Cup Naples, March 10–13, 2006
Champions Cup Boston, April 27–30, 2006
The Championships at the Palisades, September 20–24, 2006
Stanford Championships, October 4–8, 2006
Stanford Cup, November 8–12, 2006