Gregory Claeys is a British historian and political theorist. He is a professor of the History of Political Thought at Royal Holloway, University of London. He is a leading authority on the history of political thought, particularly the history of socialism and utopianism. He has written extensively on the history of socialism, anarchism, and utopianism, and has edited several collections of primary sources. He is the author of several books, including The Politics of Utopia: A Study in Theory and Practice and Machinery, Money and the Millennium: From Moral Economy to Socialism, 1815-60. He is a Fellow of the Royal Historical Society and a Fellow of the British Academy.