Urban residents depend on markets for almost all of their food purchases. Urban population growth, rising levels of urban poverty and issues affecting food supply and distribution, to and within cities, have four major consequences for urban food security. Urban and peri-urban horticulture (UPH) can be an important source of food for cities, especially when rural food production and transportation systems are underdeveloped. However, agriculture near densely populated areas poses a number of problems. Inappropriate use of chemicals and solid and liquid wastes can contaminate food, soil and water. While many problems could be solved by information and extension advice, city authorities have often responded by destroying food crops and evicting food producers from public lands.