Janssen is a surname. Notable people with the surname include:
Saint Arnold Janssen (1837–1909), German founder of the Society of the Divine WordBenno Janssen (1874–1964), American architectBenny Janssen Dutch sidecarcross riderBrian Janssen (born 1962), Australian boxer of the 1980sCasey Janssen (born 1981), American baseball player for the Washington NationalsConstant Janssen (1895–1970), Belgian founder of predecessor of Janssen PharmaceuticaDavid Janssen (1931–1980), American film and television actorFamke Janssen (born 1965), Dutch actressHorst Janssen (1929–1995), German printmakerJan Janssen (born 1940), Dutch professional cyclistJohannes Janssen (1829–1891), German historianMarco A. Janssen (born 1969), Dutch econometristPaul Janssen (1926–2003), Belgian founder of Janssen PharmaceuticaPierre Jules César Janssen (1824–1907), French astronomerRené Janssen (born 1959), Dutch nanotechnologistRik Janssen (born 1957), Dutch politicianRuud Janssen (born 1959), Dutch Fluxus and mail artistTiny Janssen Dutch sidecarcross riderVincent Janssen (born 1994), Dutch professional footballerZacharias Janssen (1580–1638), Dutch spectacle-maker; invented a compound microscope