Gerald Allan Cohen FBA (/ˈkoʊən/ KOH-ən; 14 April 1941 – 5 August 2009) was a Canadian political philosopher who held the positions of Quain Professor of Jurisprudence, University College London and Chichele Professor of Social and Political Theory, All Souls College, Oxford. He was known for his work on Marxism, and later, egalitarianism and distributive justice in normative political philosophy.

Born into an ethnically Jewish but "militantly anti-religious" family in Montreal, Quebec, on 14 April 1941, Cohen was a "red diaper baby". His mother was a longtime Canadian Communist Party member; his father had similar political views but chose not to join. Cohen was educated at the Morris Winchevsky School, Strathcona Academy, and Outremont High School. He then attended McGill University, obtaining a BA in philosophy and political science, and the University of Oxford, where he studied under Gilbert Ryle (and was also taught by Isaiah Berlin) and obtained a BPhil in philosophy.

Cohen was assistant lecturer (1963–1964), lecturer (1964–1979), then reader (1979–1984) in the Department of Philosophy at University College London, before being appointed to the Chichele chair at Oxford in 1985. Several of his students, such as Christopher Bertram, Simon Caney, Alan Carter, Cécile Fabre, Will Kymlicka, John McMurtry, David Leopold, Michael Otsuka, Seana Shiffrin, and Jonathan Wolff went on to be important moral and political philosophers. Cohen retired from the Chichele chair in 2008. At the time of his death, he was a visiting Quain Professor of Jurisprudence at UCL Faculty of Laws.

Cohen was a proponent of analytical Marxism and a founding member of the September Group. His 1978 work Karl Marx's Theory of History: A Defence defends an interpretation of Karl Marx's historical materialism its critics often call technological determinism. In History, Labour, and Freedom and Self-Ownership, Freedom, and Equality, Cohen offers an extensive moral argument in favour of socialism, contrasting his views with those of John Rawls and Robert Nozick by articulating an extensive critique of the Lockean principle of self-ownership as well as the use of that principle to defend right as well as left-libertarianism. In If You're an Egalitarian, How Come You're So Rich? (which reprints his 1996 Gifford Lectures), Cohen addresses the question of what egalitarian political principles imply for the personal behaviour of those who hold them.

Who gets what out of a market transaction reflects, among other things, the relative power of the players. Jettisoning the labor theory of value, Cohen argues that the "structure of proletarian unfreedom" requires workers to work for some capitalist. Reconceptualizing the Marxian critique of capitalism in this way turns it into an argument about power and freedom rather than labor-power and value. It suggests that, for all Marx's conceptual and predictive failures, his intuition that some under capitalism lack a basic freedom that others enjoy at their expense merits our continuing attention. But for this, it is important to solve various conceptual problems.

Cohen was known for his flamboyant style during philosophical debates. According to his best friend, the philosopher Gerald Dworkin, "Nothing was too inappropriate, private, bizarre, or embarrassing to be suddenly brought into the conversation".

In 1965, Cohen married Margaret Pearce; they had three children and divorced in 1996. Three years later, he married Michèle Jacottet. He personally abjured technology, a stance he called "technological conservatism"; Michèle answered all his email.

Cohen was close friends with Marxist political philosopher Marshall Berman.