The research group Participation, Opportunities, Structures (POS+) focusses its research on the multidimensional patters of participation and social exclusion in both current and past societies. POS+ stands for theory-driven empirical research guided by two of the major debates in sociological theory. A first is the micro-macro link, how developments at the macro-level affect phenomena and systems at lower levels, including social solidarity, forms of participation, social practices and social relations, but also how these lower level systems reproduce and transform the higher level systems. The second debate is the one on structure vs. agency, which involves issues of freedom and social order, how structures constrain and enable the behavior of groups and individuals, and how they in turn can transform structures. Issues regarding participation are also situated in more multidisciplinary research fields regarding citizenship, civil society, and the third sector.