This paper describes the scale and nature of urban poverty in low- and middle-income nations and summarizes the different approaches that have been tried to reduce it. It draws on the literature not only on poverty but also on deprivations associated with poverty – poor quality housing conditions, health risks, and lack of access to basic services, rule of law, and voice. It also presents evidence that the scale and depth of urban poverty in Africa and much of Asia and Latin America are greatly underestimated because of inappropriate definitions and measurements. How a problem is defined and measured influences how a solution is conceived, designed, implemented – and evaluated. The use of inappropriate poverty definitions that understate and misrepresent urban poverty may be one reason why so little attention has been given to urban poverty reduction by most aid agencies and development banks. It explains the paradox of many poverty statistics apparently showing little urban poverty despite the evidence showing the very large numbers living in poverty and facing many deprivations.