The 2021 Swiss Open Gstaad was a men's tennis tournament played on outdoor clay courts.

It was the 53rd edition of the Swiss Open, and part of the ATP Tour 250 Series of the 2021 ATP Tour.

It took place at the Roy Emerson Arena in Gstaad, Switzerland, from 19 July through 25 July 2021.

[1] *per team The following players received wildcards into the main draw: The following players received entry from the qualifying draw: The following players received entry as lucky losers: The following pairs received wildcards into the doubles main draw: