The existing data on international migration suffers from problems (gaps) of inconsistency in definitions and data collection methodology, lack of adequate statistics, ignorance of new data sources and limitations for comparability, among others. Additionally, given the intrinsically interdisciplinary nature of migration, there is no single theory, globally accepted by the (social) scientists. This workshop will focus on the identification of gaps in migration data systems and coherence in terms of definitions, contemporary migration dynamics, and the (missing) links to the existing theories.