Stefanos Tsitsipas is a Greek professional tennis player. He has been ranked as high as world No. 3 by the Association of Tennis Professionals (ATP), which he first achieved on 9 August 2021, making him the highest-ranked Greek player in history alongside Maria Sakkari.

The Association of Tennis Professionals (ATP) is the governing body of the men's professional tennis circuits – the ATP Tour, the ATP Challenger Tour and the ATP Champions Tour. It was formed in September 1972 by Donald Dell, Jack Kramer, and Cliff Drysdale to protect the interests of professional tennis players, and Drysdale became the first president. Since 1990 the association has organized the ATP Tour, the worldwide tennis tour for men and linked the title of the tour with the organization's name. It is the governing body of men's professional tennis. In 1990 the organization was called the ATP Tour, which was renamed in 2001 as just ATP and the tour being called ATP Tour. In 2009 the name of the tour was changed again and was known as the ATP World Tour, but changed again to the ATP Tour by 2019. It is an evolution of the tour competitions previously known as Grand Prix tennis tournaments and World Championship Tennis (WCT). The ATP's global headquarters are in London. ATP Americas is based in Ponte Vedra Beach, Florida; ATP Europe is headquartered in Monaco; and ATP International, which covers Africa, Asia and Australasia, is based in Sydney, Australia.