2021 Hamburg European Open – Women's singles

Kim Clijsters was the defending champion, having won the previous edition in 2002, but chose not to participate.

Elena-Gabriela Ruse won her maiden WTA Tour singles title as a qualifier, defeating Andrea Petkovic in the final, 7–6(8–6), 6–4.

This tournament marked Dayana Yastremska's return to professional tennis, after her suspension for testing positive for a prohibited substance was lifted by the ITF.

Seeds
The top four seeds received a bye into the second round. • # 🇺🇦 Dayana Yastremska (semifinals)

• # 🇰🇿 Yulia Putintseva (second round)

• # Tamara Zidanšek (quarterfinals)

• # 🇺🇸 Danielle Collins (quarterfinals)

• # 🇫🇷 Fiona Ferro (first round)

• # Jil Teichmann (first round)

• # 🇺🇸 Bernarda Pera (second round)

• # 🇫🇷 Caroline Garcia (first round)

Seeds
• # 🇵🇱 Magdalena Fręch (moved to the main draw)

• # 🇸🇰 Kristína Kučová (qualifying competition, lucky loser)

• # 🇷🇺 Marina Melnikova (qualified)

• # 🇷🇴 Elena-Gabriela Ruse (qualified)

• # 🇧🇬 Isabella Shinikova (qualifying competition)

• # 🇩🇪 Katharina Gerlach (qualifying competition)

• # 🇱🇺 Mandy Minella (qualified)

• # 🇦🇷 Paula Ormaechea (first round)

Qualifiers
• # 🇩🇪 Anna Zaja

• # 🇱🇺 Mandy Minella

• # 🇷🇺 Marina Melnikova

• # 🇷🇴 Elena-Gabriela Ruse

Lucky loser
• # 🇸🇰 Kristína Kučová