This paper examines the determinants of specialization in production in developed countries, developing countries and in the pooled sample. We use a dual approach to general equilibrium theory, namely the GDP function framework, and apply it to panel data. We find that factor supplies and openness to trade are important factors influencing the structure of production, but we also uncover interesting differences in results across output sectors and groups of countries. In addition, we find evidence that Hicks-neutral technological differences do not affect specialization. Finally, our results on the effect of openness highlight the sources of conflicts between developed and developing countries in multilateral trade negotiations.