There is economic evidence that diversity has consequences for economic performance (see Alesina and La Ferrara, 2005). This might have consequences for immigration policy--how many immigrants to allow into a country and from what cultural background. But, central to such a discussion is the pace of cultural assimilation among immigrants--this under-researched topic is the focus of this paper. It investigates the extent and determinants of British identity among those living in Britain and the views on rights and responsibilities in societies. We find no evidence for a culture clash in general, and one connected with Muslims in particular. The vast majority of those born in Britain, of whatever ethnicity or religion, think of themselves as British and we find evidence that third-generation immigrants are more likely to think of themselves as British than second generation. Newly arrived immigrants almost never think of themselves as British but the longer they remain in the UK, the more likely it is that they do. This process of assimilation is faster for those from poorer and less democratic countries, even though immigrants from these countries are often regarded as a particular cause for concern. Our analysis of rights and responsibilities finds much smaller differences in views between the UK-born and immigrants than within the UK-born population.