BACKGROUND The successful integration of immigrants is seen as a principal means to secure economic growth and welfare in many countries. Success in this task depends on the capacity to formulate effective integration policies, which in turn is based on research capable of describing and explaining the integration process properly. OBJECTIVE Our objective is to define a conceptual and quantifiable measure of full immigrant integration. This enables a quantitative evaluation of how integrated immigrants are in a specific context in an immigrant - native system - a question poorly addressed by past research. METHODS Our approach consists of looking at the functional dependency of different integration quantifiers on immigrant density. The empirical analysis uses register data from Spain. We focus on social integration and labour market integration in formal employment. RESULTS In our empirical analysis we find dramatic differences in immigrant integration levels across integration contexts. While labour market integration approaches the level of full integration, social integration quickly declines as immigration levels surge. It is shown that these differences are primarily due to the presence of social network effects in the social integration process, absent in the labour market integration process. CONCLUSIONS Proper identification of integration deficits and its causes is likely to improve the efficiency of integration policy making, and the capacity to reach integration targets. Our framework has this quality. The research presented here shows that full labour market integration of immigrants is a realistic target. However, it also shows that, if left unattended, the segregation forces contained in social networks, quite dramatically obstruct the social integration process.