`titrebSummary`/titrebThe material reality of cities or the experiences which they provide have always been compared. Nowadays comparison is made in an abstract manner by using the criteria and indicators of evaluation. The economic and spatial reality of the city which is specific and can be grasped is declining. There is an ever-increasing tendency for the city to exist through the actions which are carried out on it; as a result, the city is affected by the uncertainties and the discussions which bear on the legitimacy, the effectiveness and the modes of public action and sustains the demand for evaluation and its expertise. The marked development of competition between cities has led to the elaboration of tools for measuring (classification, etc.) their competitive capacities. This apparatus of evaluation which dissects and abstracts may seem to destroy urban reality and its unity. But is also enables reconstruction, in an incomplete manner and one which is worth discussing, an urban object which in any event no longer exists. For urban sociology, the theoretical and methodological debate on the modes and contents of evaluation assumes a central character and is part of a sociology of urban action which should be promoted.