With their socio-physical, socio-economic, sociocultural, and sociopolitical presence cities have always been highly differentiated spaces expressive of heterogeneity, diversity of activities, entertainment, excitement, and pleasure. they have been (and still are) melting pots for the formulation of and experimentation with new philosophies and religious and social practices. they produce, reproduce, represent, and convey much of what counts today as culture, knowledge, and politics. Urban spaces within cities are no exception; they are places for the pursuit of freedom, un-oppressed activities and desires, but also ones characterized by systematic power, oppression, domination, exclusion, and segregation. in dealing with these polar qualities diversity has become one of the new doctrines of city planners, urban designers, and architects. it continues to be at the center of recent urban debates. Little is known, however, on how urban space diversity can be achieved. in recent rhetoric, diversity denotes in generic terms a mosaic of people who bring a variety of ethnic and cultural backgrounds, styles, perspectives, values and beliefs as assets to the groups and organizations with which they interact. however, in urban discourses it has been addressed as having multiple meanings that include mixing building types, mixing physical forms, and mixing people of different social classes, racial and ethnic backgrounds. While some theorists attribute diversity to the socio-physical aspects of homogeneity within heterogeneity, social differentiation without exclusion, variety, and publicity, others associate it with socio-political aspects of assimilation, integration, and segregation. While some of these meanings represent a concern for a specific group of professionals including architects and urban designers, urban planners, cultural analysts and abstract theorists, they all agree that each meaning or aspect of diversity is linked to the others; they all call for strategies for urban development that stimulate socio-physical heterogeneity. With the goal of unveiling lessons learned on urban diversity from various cases in different parts of the world, this issue of Open house international selects ten papers after a rigorous review process. the edition encompasses several objectives. it aims at providing a conceptualization of urban diversity while articulating its underlying contents and mechanisms by exploring the variety of meanings adopted in the urban literature. in essence, it attempts to establish models for discerning urban space diversity while mapping such models on selected case studies from europe, african, and the Middle east.