Urban agriculture (UA) has a long tradition in many countries worldwide, is actively engaging about 800 million people, and is now increasingly considered by urban planning and land-use personnel. Urban cropland, in particular, covers more than 67 Mha or more than 5% of the total global cropland area. Urban agriculture practices have many benefits and, in particular, may contribute to food security of urban dwellers by providing vegetables and fruits. However, growing food in urban ecosystems and, especially, on degraded urban soils is challenging, and research on UA in the past has focused on the social sciences. Although the number of studies on urban soils has increased strongly during the last two decades, much work needs to be done as many urban areas have been neglected in previous studies. The needs and benefits of UA and organic agriculture such as building up natural resources through biological mechanism and recycling of wastes, keeping the nutrients cycle within the system, strengthening communities, and improving human capacity are interconnected. Thus, more research is needed on how to maintain or enhance urban soil fertility by soil and land-use management practices. This knowledge must be disseminated among urban gardeners and farmers for improving UA and organic UA systems. Transdisciplinary approaches involving practitioners, urban dwellers, planners, policy makers, and, especially, soil scientists are needed to enhance UA production.