Jan Zieliński is a Polish professional tennis player who specializes in doubles. He has an ATP career-high doubles ranking of world No. 7, which he attained on 19 June 2023. His highest ranking in singles has been No. 769, achieved on 20 September 2021. His best results at Grand Slam events have been reaching the final of the 2023 Australian Open doubles with Hugo Nys and winning the 2024 Australian Open mixed doubles alongside partner Hsieh Su-wei.

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.