Lassen is a Danish and Norwegian patronymic surname meaning "son of Lars" (equivalent of Laurentius), and thus a parallel form of the more common surname Larsen. Notable people with the surname include:
- Anders Lassen (1920–1945), Danish recipient of the British Victoria Cross
- Christian Lassen (1800-1876), Norwegian-German orientalist
- Christian Riese Lassen, American artist known for marine art
- Clyde Everett Lassen, United States Navy aviator and Medal of Honor recipient
- Eduard Lassen, Belgian composer
- Erik Sætter-Lassen (1892–1966), Danish sport shooter
- Georg Lassen, German U-boat captain
- Hartvig Lassen (1824–1897), Norwegian editor and literary historian
- Henrik Andreas Zetlitz Lassen, Norwegian politician
- Inger Lassen (1911–1957), Danish actress
- Jean Elisabeth Lassen, Canadian weightlifter
- Justin Lassen, American composer, producer, multi-instrumentalist and remixer
- Leigh Lassen, American actress
- Leo Lassen (1899–1975), American baseball announcer
- Niels A. Lassen (1926–1997), Danish medical researcher
- Peter Lassen, Danish-American rancher, prospector and explorer
- Peter Lassen (footballer), Danish football player
- Werner Lassen, Namibian golfer
Lassen may also refer to Lassen Peak, located in Lassen Volcanic National Park, a national park in the United States.
See also
- Larsen (disambiguation)
- Larson (disambiguation)