Due to migration, many contemporary European societies have become increasingly diverse. Ethnic and religious differences have increased and questions related to cultural diversity are strongly debated in the social sciences and in societies more generally. Problems of social cohesion and a lack of solidarity with other ethnic or religious groups have come to the fore. These problems become manifest in patterns of exclusive social identifications and in unfavorable attitudes and discriminatory behavior towards other ethnic and religious groups. This research line addresses a core question of social theory, namely, the problem of identity and social cohesion, by studying processes that facilitate and hamper the development of exclusive and inclusive social identifications and the mechanisms involved in intergroup conflicts. More precisely, the research line focuses on how social and cultural conditions affect identification patterns and interethnic and interreligious relations. Social identities provide a shared perspective on social reality and involve tendencies for intergroup differentiation and exclusionary behavior. Major developments during the review period have been the increased focus on religious differences in addition to ethnicity, and the testing of hypotheses in different countries and among different age groups including early adolescents. The interrelationships between ethnic and religious identity and the development of interethnic and interreligious conflicts within different national and local contexts will be core issues for future research.

Coherence of the research line derives from systematic use of a shared theoretical perspective and common tools of investigation. Theoretically, the research line builds upon theories that have been developed in sociology and social psychology. Hypotheses are tested by survey research and experimental questionnaire designs. Two features make this research line original and significant. First, the research line contributes to the elaboration of sociological theories by specifying and examining the social psychological mechanisms involved in interethnic and interreligious relations. Second, the research line examines the same mechanisms and tests the same hypotheses in different national and cultural settings, such as the Russian Federation and in countries in Eastern and Western Europe, as well as in different regions, cities, neighborhoods, and institutions in the Netherlands.

The research line has developed from the research program of the European Research Center on Migration and Ethnic Relations (ERCOMER), initiated by Hagendoorn. During the review period, the group of senior researchers also included Verkuyten, Phalet, and Komter. The research line maintains the monthly ERCOMER-seminar. Major research grants obtained during the review period include a study on The Quest for Ethno-National Identity: Positive and Negative Effects (principal investigator: Hagendoorn), funded by INTAS and Ethnic Identity and Religious Mobilization of the European Second Generation (principal investigator: Phalet), funded by NORFACE. Komter is co-applicant of the Netherlands Kinship Panel Study that is subsidized through an NWO Large Investment grant (see below: research line Households and Employment). Representative publications during the review period are an article by Verkuyten (2005) in Journal of Personality and Social Psychology, an article by Sniderman, Hagendoorn & Prior (2004) in American Political Science Review and Verkuyten's monograph The Social Psychology of Ethnic Identity (Psychology Press 2005).