Fenster is a surname, from the German language word for "window". Notable persons with this surname include:

• Della Dumbaugh, formerly Della Fenster, American historian of mathematics
• Aaron Fenster, Canadian engineer
• Ariel Fenster (born 1943), Canadian science promoter and lecturer at McGill University
• Boris Fenster (1916–1960), Russian dancer, choreographer and ballet master
• Darren Fenster (born 1978), American baseball player and coach
• Fred Fenster (born 1934), American metalsmith
• Gigi Fenster, South African-born New Zealand author, creative writing teacher and law lecturer
• Julie M. Fenster (born 1957), American author of historical articles and books
• Mark Fenster, American lawyer and author in Florida
• Saul Fenster, president of New Jersey Institute of Technology during 1978–2002
• Karol Martesko-Fenster, American media executive
• Leon Fenster, British artist

• Arch Fenster, a character in the American 1962–63 sitcom I'm Dickens, He's Fenster
• Fred Fenster, a character in the 1995 film The Usual Suspects

• Fenster, another name for a tectonic window (a geologic structure)
• Fenster School, American school in Catalina Foothills, Arizona
• Schnell Fenster, Australian band, active 1986–1992
• "Tausend Fenster", Austrian entry in the Eurovision Song Contest 1968