The 2021 ATP Finals (also known as the 2021 Nitto ATP Finals for Nitto sponsorship) was a men's tennis year-end tournament played on indoor hard courts at the Pala Alpitour in Turin, Italy, from 14 to 21 November 2021.

It was the season-ending event for the highest-ranked singles players and doubles teams on the 2021 ATP Tour.

This was the 52nd edition of the tournament (47th in doubles), and the first time Turin hosted the ATP Tour year-end championships.

Provisional rankings are published weekly as the ATP Race to Turin, which only counts events played in 2021.

Furthermore, players who finished 2020 in the world's top 30 are commitment players who must (if not injured) include points for the 8 mandatory Masters tournament regardless of whether they enter, and who must compete in at least 4 ATP 500 tournaments (though the Monte Carlo Masters may count to this total), of which one must take place after the US Open.

Players may have their ATP Tour Masters 1000 commitment reduced by one tournament, by reaching each of the following milestones: If a player satisfies all three of these conditions, their mandatory ATP Tour Masters 1000 commitment is dropped entirely.

[23] * Ranking points in italics indicate that a player used a better result than in a Grand Slam or Masters 1000 tournament, because all events were non-mandatory this season.