Contemporary migration has entailed the emergence of new forms of multilingualism in many European cities. The article uses the concept of complex diversity to analyse this dynamic. The concept points at settings where historical forms of multilingualism and more recent patterns of linguistic heterogeneity interact in ways that lead to particularly rich cultural configurations. The authors assess how local authorities deal with multilingualism in three cities that represent ‘most complex’ cases of diversity politics: Barcelona, Luxembourg and Riga. The focus is on policies related to public communication and on the approaches adopted to promote social and political inclusion in ever more multilingual urban environments. In normative terms, the article concludes that political responses to complex diversity should aim both at overcoming linguistic status inequalities based on historical structures of domination and at creating common spaces of communication for diverse citizens.