The purpose of this study is to describe the development of philosophy in Poland since the end of the Second World War and the development of Marxist-Leninist philosophy which, owing to international political events, has assumed an impor tant role in the intellectual life of contemporary Poland. This task could not have been accomplished without relating post-war developments to those of the inter war period. Consequently, the period studied covers the years 1918-1958. Yet another extension was necessary. Marxism-Leninism regards sociology as a part of philosophy. Moreover, Marxism-Leninism often resorts to sociology to support or justify some of its philosophical views. Finally, its criticism of 'bourgeois philosophy' is often concerned with social philosophy and socio logical theories which supposedly are implicit or explicit in 'bourgeois philoso phy'. For this reason it was desirable to consider in this study some theoretical and methodological problems of the social sciences. They are taken into ac count when they illuminate philosophical controversies or the evolution of Marxist-Leninist philosophy. Marxism-Leninism is not only a new line of development but also a new point of departure in Polish philosophy. It provides a striking contrast with the established philosophical tradition which originated roughly at the time when G. E. Moore and Bertrand Russell initiated the analytical trend in English philosophy. The contrast can be epitomised by the contradistinction of philoso phy and ideology, chosen as the title of this study.