The theory of migration systems of which rapid ascent was stimulated above all by the support of the International Union for the Scientific Study of Population (IUSSP), emerged above all to make a step further with the help of it in researching international migrations. It was to answer numerous questions concerning migrations: why migration streams develop and change in the course of time, why they occur in certain states, why some people migrate and others do not; how political, economic, social and other relations among different nations contribute to the development of the migration system; how international movements interact on other international swims of goods, capital, information, technology; how migrants develop and use supranational family and social nets... The contribution tries to estimate the degree of successfulness of the theory and its present influence on researches of international migrations.