The study describes the migration data collection systems and their legal backgrounds within the European Union, it analyses the parallel data collection systems and the background of their development. One of the tasks of the study is to introduce the reader into the policy of home- and justice affairs of the EU which enables the interoperability between the EU systems, it describes the effect of interoperability of the data query and data collection practice. At the end the author gives some advices which can serve for a more efficient data collection system in the EU.