Article dans une revue: Conventional aggregate trade elasticity estimates hardly vary across countries. We introduce an aggregate elasticity that is implied by theory: It is the value that equates the welfare gains from trade as implied by one- and multi-sector versions of the model in Arkolakis et al. (American Economic Review, 102 (2012):94–130). These estimates are predicated on sector-level values for trade elasticites, which we provide at three-digit levels for 28 developed and developing countries. The values for this aggregate elasticity vary greatly across countries, and they do so because of countries' patterns of production and because a given sector-level elasticity displays considerable cross-country heterogeneity.