This paper focuses on residential sorting by social and ethnic status in large French urban areas. Our objective is to assess the relative importance of two major determinants of segregation stressed by the economic literature (Bartolome and Ross, 2003; Brueckner et al., 1999): (i) Alonso sorting over space, due to the trade-off between land consumption and accessibility to the central city and (ii) Tiebout sorting over jurisdictions, due to the taste for local public goods and by extension for all kinds of local public amenities (e.g. neighborhood externalities). Our methodology draws on Schmidheiny (2006). First, a conditional logit model is estimated for each urban area, in which moving households are assumed to sort based on jurisdiction distance to the central city and jurisdiction mean of households' incomes (as a proxy for the level of public amenities). Second, our estimation results are used to simulate the counterfactual residential patterns that would prevail if, alternatively, one or the other of these mechanisms were inactive (setting the coefficients of the corresponding variables to zero). The contribution of each mechanism to the observed social and ethnic segregation is finally appreciated by comparing the values of dissimilarity indexes computed on the basis of the counterfactual households distributions and on the observed households distribution. Tiebout-sorting emerges as the primary cause of social segregation among wage-earning households. On the contrary, Alonso-sorting appears to be the main driver of segregation between economically active and inactive households, as well as between French-citizen and Foreign-citizen households.