This paper aims to map out the consequences of migration flows for modern cities, and in particular it analyzes various aspects of urban cultural diversity. It argues that the sustainable and innovative development of cities under conditions of creative cultures is possible, and it presents a ‘pentagon model’ as an analytical tool for investigating the necessary conditions for achieving a balanced and thriving urban development. The paper also pays attention to the socio-economic aspects of urban pluriformity caused by the emergence of ethnic or migrant entrepreneurs. The paper presents an integrated overview of the advantages and drawbacks of cultural diversity in relation to mass migration inflows into modern cities. A major part of the paper is devoted to the positive and negative socio-economic implications of cultural diversity. To that end, a series of extensive survey tables is provided. Finally, the relationship between diversity and innovativeness is addressed.