Johannsen is a surname. Notable people with the surname include:
Franz Johannsen (born 1921), German sprint canoeist who in the 1950sGunnar Johannsen (born 1940), German cyberneticist, and Professor of Systems Engineering and Human-Machine SystemsHans Johannsen (1913–1961), German chief engineer on a U-boat in World War IIHelmuth Johannsen (1920–1998), German football coachJake Johannsen (born 1960), American comedianKristoffer Johannsen (born 1977), Danish former professional football playerKurt Johannsen (1915–1944), German Schnellboot commander in World War IINicholas Johannsen, German-American amateur economistStian Johannsen, Norwegian musician, bassist for the black metal band MayhemOskar Augustus Johannsen (1870–1961), American entomologist, specialist of DipteraWilhelm Johannsen (1857–1927), Danish botanist, plant physiologist and geneticist