The goal of this project is to study linguistic complexity in three different areas: formal grammar, language acquisition, and sociolinguistics. The groundbreaking part of this project is that it will attempt to combine these different sub-disciplines of modern linguistics. Different methodologies and theoretical perspectives will be useful in order to illuminate complementary aspects of language complexity and thus contribute to deepening our understanding of this important phenomenon. A unifying aspect of the research will be the use of multilingual data. These data have become increasingly important for linguistic methodologies and theories, but also for public policy makers in the sense that they address consequences of migration and children growing up acquiring parts of multiple languages. Some of the research conducted in the LCIS project will most likely inform educational policies and as such contribute to important debates about multilingualism in the public sphere.