This concise and accessible introduction brings the writings of Marx and Engels and later thinkers in the Marxist tradition including Althusser, Gramsci, the Frankfurt School as well as Liberation Theologians such as Gutierrez and Maduro, into focus in relation to questions of religion, social change and social justice. Marx was a nineteenth century thinker trying to develop a theory that could explain the dramatic social and technological changes that he lived through. Later thinkers modified and developed key elements of Marx' theoretical model, with religion - particularly Christianity - providing a vital point of critical self-reflection for thinkers in the Marxist tradition. This book tracks these modifications and developments to Marx' ideas, and their continuing relevance to contemporary debates about religion, social change and social justice.