In current welfare state analysis there is little theory to explain th
e action of exclusive groups. This article explores the possibilities
of a theory that focuses on the interaction between individual choices
and strategies, the formal systems, policies and rules of governments
and the informal norms and practices of groups. The argument is that
club theory, a branch of public choice concepts, represents a promisin
g new element in such an approach. A theoretical frame has to account
for both collectivisation and fragmentation processes - how mass solid
arities in welfare states come to be created and in turn to be broken
up into narrower mutualities. Migration is used as an example to show
how the actions of migrants and policy decisions about them affect the
se dynamics or are affected by them.