Terms such as transnational social spaces, transnational social elds or transnationalism usually refer to sustained ties of persons, networks and organizations across the borders across multiple nation-states, ranging from little to highly institutionalized forms. However, there are two large conceptual gaps in the study of transnational social spaces arising out of international migration and refugee ows. First, terms such as transnational social spaces and transnational communities are often

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... sed synonymously, as if 'transnational community' were the only form or type of transnational social space. This analysis outlines the primary mechanisms operative in transnationalization: reciprocity in small groups, exchange in circuits and solidarity in communities. These mechanisms correspond to distinct types of transnational social spacestransnational kinship groups, transnational circuits and transnational communities. Second, the implications of transnationalization for citizenship and culture have not been systematically explored. The concept of border-crossing expansion of social ties also helps to enrich our understanding of immigrant integration in the political and cultural realms. There is an elective af nity between the three broad concepts to explain and describe immigrant adaptation: assimilation, ethnic pluralism and bordercrossing expansion of social space, on the one hand, and the concepts used to describe citizenship and culture, on the other hand. In the political realm the concepts are national, multicultural and transnational citizenship; and in the cultural sphere, acculturation, cultural retention and transnational syncretism.