This thesis represents an original contribution to research in offering a comprehensive analysis of the work of Rudolf Bahro. The thesis combines a study of Bahro's work as a prominent opposition figure in the German Democratic Republic in the 1970s with an assessment of his career as an outspoken member of the West German Green Party in the 1980s. The core of the thesis is devoted to a thorough reappraisal of Bahro's major critique of 'actually existing socialism' in East Germany, Die Alternative - Zyr Kraik des real existierenden Sozialismus. Bahro's harsh critique of the SED is explored within the context of the GDR's historical development and Eastern European Marxist revisionism in general. A critical analysis of the extensive secondary literature which now surrounds this work is undertaken to discover how far existing interpretations offer an accurate assessment of Die Alternative. A further section compares for the first time the differing reception of Bahro's study in both East and West Germany. Bahro's earliest essays as an editor of the GDR journal Forum and his first critical work ... die nicht mit den Wolfen heulen are discussed as a key to establishing the particular nature of his opposition. Later chapters trace the development of Sahro's theories and discuss his contribution to the peace and ecology debates in West Germany in the 1980s. Bahro's efforts to achieve a synthesis of the interests of ecology and socialism are explored and his 'Fundamentalist' version of Green politics is discussed within the context of the Green Party's early development. The thesis concludes with an assessment of the increasingly radical utopianism permeating Bahro's writings and offers a critical examination of his attempts to infuse the ecology debate with a spiritual dimension, as detailed in Logik der Rettung, his chief work written in West Germany.