Although models with factor price equalization are used frequently in
both theoretical and applied research in international economics, only
sufficient conditions for factor price equalization have been present
ed in the literature. In this paper, we present necessary and sufficie
nt conditions for FPE under quite general assumptions about the techno
logies of different countries. The necessary and sufficient conditions
we derive are consistent with joint production, decreasing returns to
scale, and substantive differences in the technologies and endowments
of different countries. Our results enable us to reconcile the classi
cal approach and the integrated equilibrium approach to factor price e
qualization.