The 2021 MercedesCup was a men's tennis tournament played on outdoor grass courts.

It was the 43rd edition of the Stuttgart Open, and part of the ATP Tour 250 series of the 2021 ATP Tour.

It was held at the Tennis Club Weissenhof in Stuttgart, Germany, from 8 June until 13 June 2021.

Unseeded Marin Čilić won the singles title.

*per team The following players received wildcards into the main draw: The following players received entry from the qualifying draw: The following player received entry as a lucky loser: The following pairs received wildcards into the doubles main draw: The following pairs received entry as alternates: