Urbanization destroys or modifies native habitats and creates new ones with its infrastructure. Because of these changes, urban landscapes favor non-native and native species that are generalists. Nevertheless, cities reveal a great variety of habitats and species, and, especially in temperate cities, the diversity of vascular plants and birds can be higher than in the surrounding landscapes. The actual occurrence of a species, however, depends on habitat availability and quality, the spatial arrangements of habitats, species pools, a species’ adaptability and natural history, and site history. In addition, cities are particularly human-made ecological systems. Top-down and bottom-up activities of planners, land managers, and citizens create the urban biodiversity in general and in detail. Plants and animals in cities are the everyday life contact with nature of the most humans on our earth. The intrinsic interplay of social and ecological systems with a city often forms unique biotic assemblages inherent to that city. To support native biodiversity, landscape architects, conservation biologists, and other groups are linking landscape design with ecosystem structure and function to create and restore habitats and reintroduce native species in cities.