Dennis Patkin Altman (born 16 August 1943) is an Australian academic and pioneering gay rights activist.
Altman was born in Sydney, New South Wales to Jewish immigrant parents, and spent most of his childhood in Hobart, Tasmania. In 1964 he won a Fulbright scholarship to Cornell University, where he began working with leading American gay activists. Returning to Australia in 1969, he taught politics at the University of Sydney, and in 1971 he published his first book, Homosexual: Oppression and Liberation—considered an important intellectual contribution to the ideas that shaped gay liberation movements in the English-speaking world. Among his prophetic constructions were "the polymorphous whole" and his posing of the notion of "the end of the homosexual", in which the potential for both heterosexual and homosexual behaviour becomes a widespread cultural and psychological phenomenon. In 2005 he published Gore Vidal's America, a study of US author Gore Vidal's writings on history, politics, sex, and religion.
In 1985 Altman moved to La Trobe University, where he later became professor of politics. He was appointed the Visiting Chair of Australian Studies at Harvard University from January 2005. Since 2009 Altman has been the director of the Institute for Human Security at La Trobe University.
Altman has delivered speeches on the topic of sexual liberation. One of his most known speeches, Human beings can be much more than they have allowed themselves to be, was delivered at the first Gay Liberation Group meeting at the University of Sydney on 19 January 1972.
In his preface to The City and the Pillar, Gore Vidal writes that Altman brought the book back with him but it was seized at Sydney Airport and subsequently declared obscene by a judge who also observed that the Australian obscenity law was "absurd", thus leading to its repeal some time later.