This first modern study provides an original and balanced perspective of a theorist whom Lenin referred to as both 'master of Marxism' and 'renegade'. Examining Kautsky's political thought over a period stretching from the Paris Commune to the Second World War, the author argues for the consistency with which Kautsky developed his positions on socialism, democracy, political parties and the role of the proletariat. While Salvadori's analysis is grounded in the debates within the Communist International and the German labour movement, Kautsky emerges as a distinctly modern thinker who produced a Marxist theory of the state, and originated critique of the USSR as a 'state capitalist' system. At this level, it provides a serious and measured exposition of the terms on which arguments for socialist strategy currently move.