The 2021 Stockholm Open was a professional men's tennis tournament played on indoor hard courts. It was the 52nd edition of the tournament, and part of the ATP Tour 250 series of the 2021 ATP Tour. It took place at the Kungliga tennishallen in Stockholm, Sweden from 7 to 13 November 2021. Unseeded Tommy Paul won the singles title.
Paul won his first ATP Tour title.
The following players received wildcards into the singles 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:
The following pairs received entry into the doubles main draw as alternates: