During the mid XX th century the former outskirts of Barcelona was the field of an unprecedented urbanization process addressed to housing purposes. A very heterogeneous system of settlements occupied the steep hillsides of Tres Turons and Collserola. These former deprived residential suburbs became, in less than twenty years, fully urban neighbourhoods with extreme densities and urgent needs. From beginning the 80’ to our days “Barcelona on slope” has become the conceptual and physical frame for urban renewal policies. Although there’s still much to do, the large amount of accomplished plans and actions calls for an evaluation and a synthesis from which probable criteria for future actions can be inferred.