This thesis approaches the concept of integration from two different angles. The first angle is a general theoretical sociological one presented in the first part of the thesis. The second approach refers to the sociology of migration and an interdisciplinary field dealing with the integration of migrants in modern societies. After reviewing the theoretical approaches, this thesis offers an insight into contemporary policies and research on the integration of immigrants in Croatia and in the world. The central part of the thesis presents an empirical research aimed at determing how local actors involved in the process of immigrant integration understand the concept of migrant integration and how they understand their role as well as the role of wider society in this process. The research was conducted in Zadar by the means of 12 semi-structured interviews in July and August 2020 with respondents from organizations and institutions that are implementing or should implement integration measures. Finally, it is concluded that local actors understand the process of immigrant integration as Alexander (2001) describes the assimilation mode of incorporation. According to this mode, immigrants should be legally granted all civil rights, and they are expected to keep their cultural and religious practices in the private sphere.