This chapter presents the principal factors responsible for international migrations by Poles in the post-war period. It attempts to prove that the migration policy of the Polish state was the prime determinant of international migrations from communist Poland. Poland has been and does remain a country of fairly intensive emigration. During the entire post-war period, migration waves from Poland either intensified or abated depending on the socio-political situation in the country. The liberalisation of Polish state policy after 1989 coincided with the imposition of direct or indirect restrictions on foreign workers or on migration based on ethnic claims in northwestern European countries. Knowledge about migration from Poland after the Second World War is insufficient and the official statistical registries are deficient. Cross-border migrations by Poles, which assumed a mass scale precisely during that period, were an extremely grave consequence of the social, political and economic crisis that hit Poland in the 1980s.