The author analyses the factors that decisively influenced the social policy development of the West from the Middle Ages to the middle of the twentieth century. The author also distinguishes three crucial determinants of social policy development: the processes of modernisation of western societies, the organisation and mobilisation of workers and lower social strata, and the autonomous activity of the state. He also refers to different writers who, in their explanation of social policy development, have given preponderance to one of these three factors. In addition, the author points to the role of religion in social policy development because of its impact on the basic values of the population, particularly the formation of both the state and social policy. The author also stresses the influence of the war and of the economic crises on social reforms, aimed at overcoming the difficult situation in society. In the conclusion, the author proposes a multifactorial approach in the explanation of social policy development because it is most suitable for the complex circumstances in which the social policy has developed.