Despite increasing numbers of immigrants worldwide, the development of bi- or multilingual children who begin to learn two or more languages within the first three years of life remains understudied. In particular, studies on bilinguals’ executive functions (EF) and socioemotional development in preschool and early school ages still fail to provide clear pictures of how these two areas develop and how they interrelate (either due to inconsistent findings or limited studies). As EF and socioemotional development each entail different subcomponents, the use of different indicators and/or the use of different kinds of measures (performance-based or reported measures) may contribute to the inconsistent findings. Furthermore, confounds (relating, e.g., to family’s socioeconomic status: SES), aspects of study design, and various factors contributing to bilingual heterogeneity might modulate bilinguals’ EF and socioemotional development along with the relations between the two. This project aims to provide comprehensive examinations of bilinguals’ EF and socioemotional development across countries by (a) addressing the role of different facets of SES (e.g., parental educational level, family income) in the association between bilingualism and EF, (b) investigating how cultural differences and differences in bilingual language exposure moderate the association between bilingualism and children’s socioemotional development, and (c) exploring the different patterns of association between these two developmental areas across countries. Drawing on five cross-continental nationally representative data sets, which cover a wide range of broadly comparable measures and heterogeneous samples, this project will conduct secondary analyses (e.g., structural equation modeling, propensity score matching method, multigroup analysis) to study the abovementioned research questions.