Horstmann is a surname. Notable people with the surname include:
Carl Horstmann, editor of the Middle English South English LegendaryCay Horstmann, the author of several computer programming books and the creator of the Horstmann indent styleDennis Horstmann, see Special D.Dorothy M. Horstmann (1911–2001), American epidemiologist, virologist and pediatricianIgnatius Frederick Horstmann (1840–1908), American Roman Catholic bishopKai Horstmann (born 1981), English rugby union playerKen Horstmann (born 1971), American actorOscar Horstmann (1891–1977), American baseball playerRoy Horstmann (1910–1998), American football playerSidney Horstmann (1881–1962), British automotive engineer and businessmanUlrich Horstmann (born 1949), German literary scholar and writer