Janssen is a surname. Notable people with the surname include:
Saint Arnold Janssen (1837–1909), German founder of the Society of the Divine Word
Benno Janssen (1874–1964), American architect
Benny Janssen Dutch sidecarcross rider
Brian Janssen (born 1962), Australian boxer of the 1980s
Casey Janssen (born 1981), American baseball player for the Washington Nationals
Constant Janssen (1895–1970), Belgian founder of predecessor of Janssen Pharmaceutica
David Janssen (1931–1980), American film and television actor
Famke Janssen (born 1965), Dutch actress
Horst Janssen (1929–1995), German printmaker
Jan Janssen (born 1940), Dutch professional cyclist
Johannes Janssen (1829–1891), German historian
Marco A. Janssen (born 1969), Dutch econometrist
Paul Janssen (1926–2003), Belgian founder of Janssen Pharmaceutica
Pierre Jules César Janssen (1824–1907), French astronomer
René Janssen (born 1959), Dutch nanotechnologist
Rik Janssen (born 1957), Dutch politician
Ruud Janssen (born 1959), Dutch Fluxus and mail artist
Tiny Janssen Dutch sidecarcross rider
Vincent Janssen (born 1994), Dutch professional footballer
Zacharias Janssen (1580–1638), Dutch spectacle-maker; invented a compound microscope
