Based on a study of the literature on Kautsky and Kautsky's own writings from the 1880s to 1919, i.e. the period in which Kautsky took actively part in the politics of the German and international socialist movement as the authoritative Marxist theoretician, the thesis analyses the relationship between theory and practice in Kautsky's thought. The point of departure is the present dispute as to whether Kautsky's political-theoretical development is to be regarded as one of continuity or one of rupture. Both views are rejected by an alternative strategical-theoretical approach, the main argument of which is that political theories and related strategies must be seen as determined by basic theoretical conceptions on one hand and by analyses of current economic, social, political and ideological conjunctures on the other. So, the conclusion is that the actual changes in Kautsky's positions are caused by his changing conceptions of the conjuncture and are consistent with his underlying theory of Marxism.