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This paper examines urban public policies for deprived areas in the light of urban economics theories and their lessons for the socio-economic organization of cities.While improving living conditions is indeed a factor in enhancing the socio-economic standing of urban neighbourhoods, the process operates by attracting wealthier new inhabitants and driving out the existing poorer ones. We emphasize that urban economics struggles to demonstrate the emergence of stable mixed urban patterns.Either such patterns must be considered as transitional stages between two states of equilibrium in terms of segregation or attempts must be made to establish sustainable positive social interaction between privileged and deprived households within neighbourhoods.Lastly, public action to promote urban regeneration, although subject to criteria of equity, enhances neighbourhood property values and may seek out leverage effects from private actors.The final question seems to be that of city-wide transformation : it is pointless reasoning on the scale of deprived neighbourhoods as if they were isolated.Geographical “lock-in” causes friction that detracts from the success of area-specific policies. And conversely, social opening-up is not geographically neutral because policies can only transform the geography of urban segregation.Classification JEL : H31, R2, R31, R38, R58.