Knudsen refers to:

• Persons
• Gunnar Knudsen (1848–1928), Prime Minister of Norway 1908–1910 and 1913–1920
• Jens Martin Knudsen (1930–2005), Danish astrophysicist
• Keith Knudsen (1948-2005), musician, member of The Doobie Brothers
• Knud Knudsen (1812–1895), Norwegian linguist
• Konrad Knudsen (1890–1959), Norwegian painter, journalist, and parlamentarian
• Lars Knudsen (1962–), Danish researcher in cryptography
• Martin Knudsen (1871–1949), Danish physicist
• Per Holm Knudsen (contemporary), Danish author
• Semon "Bunkie" Knudsen (1912–1998), American automobile industry executive
• Valdemar Knudsen (1819–1898), Norwegian-American sugar planter on Hawaii, entrepreneur
• William S. Knudsen (1879–1948), Danish American automobile industry executive
• Other
• Knudsen Gas, scientific model for gases
• Knudsen number, mathematical ratio
• Knudsen, a brand of dairy products, currently owned by Kraft Foods