The purpose of the project is to address the complex interplay between family processes, vulnerability and well-being in Eastern and Northern Europe in the 21st century. Increasing uncertainty due to economic crises, pandemic and geopolitical tensions, paralleled by substantial changes in family patterns, provide the rationale for the project. The findings will contribute to the knowledge base on well-being for evidence-based policy-making to ensure sustainable societal development. Similarities and diversities of countries within and across these regions with respect to demographic patterns, economic and social developments, and welfare arrangements influencing well-being, provide justification for our innovative comparative research design. We address both material and subjective well-being, while recognizing vulnerability as a specific element in the linkages between family patterns and well-being. We analyze large-scale survey data with sophisticated analytical techniques. First, we study the cross-sectional association between various partnership statuses, and vulnerability and well-being in the Baltic countries, Czechia, Poland and the Nordic countries for ages of late 20s to late 50s. Relying on a longitudinal approach, we then analyze how changes in partnership statuses affect well-being, explicitly accounting for vulnerability. We also highlight if the mechanisms uncovered are gender specific, and diversities between native and foreign-born populations.