People and politics in many western countries appear increasingly hostile to immigration and cultural diversity. Multicultural discourses have been abandoned as public concern rises about European countries becoming too ethnically diverse. Opponents of multicultural approaches believe that western democratic values will be destroyed by too many immigrants whose cultures, religions and values are seen to be either too different or inferior. The claim that diverse values may threaten national identity and damage social cohesion has moved from the far-right periphery to the centre of European politics. Discourses about difference have become more exclusionary and nationalistic, while social cohesion is often being redefined to equate with homogeneity and assimilation. My analysis indicates that these changes point to a deeper underlying social process, namely that social solidarity has changed irreversibly over the past 50 years. I will examine the theoretical underpinnings of solidarity: its meaning, its contexts and foundations. Then I will explore some of the major social transformations of the past 50 years that have altered European collective identities and impacted on notions of solidarity. I conclude by considering whether the current push for 'integration and cohesion', for controlling difference, has any chance of achieving its desired outcomes.