2021 Reprint of the 1937 Edition. Reform or Revolution is the classic statement of the position of scientific socialism on the questions of capitalist development, 'historical necessity, ' social reforms, the State, democracy and the character of the proletarian revolution. It was written in criticism of the ideas presented by Eduard Bernstein, a proponent of more gradual change or "reform" as opposed to orthodox theories of revolution as espoused by Marx and Luxembourg. At the age of twenty-seven, she had established herself as a major figure in the Second International by offering one of the most comprehensive criticisms of Bernstein's revisionist call to prioritize the method of reform over that of revolution. A close friend and collaborator of Engels, a Marxist of impeccable credentials but also a pioneering advocate of gay rights, Bernstein was also the first to articulate a non revolutionary path to socialism in what is widely considered the founding text of modern social democracy: The Preconditions of Socialism and the Tasks of Social Democracy (1899). At stake in Bernstein's dilemma, she argued, was not just a tactical choice, a mere discussion about this or that method of struggle; it was the "very existence of the Social Democratic movement" as a distinctive force in the struggle against capitalism.