This text addresses the empirical validity of the factor proportions theory, based on extensive data. Departing from Heckscher-Ohlin-Vanek theory, it extends existing models by allowing factor productivities and factor prices to differ across countries. The book reformulates ranking proportions derived from Heckscher-Ohlin-Vanek equations and, based on these models, it empirically investigates, in a cross-industry framework, the patterns of international trade for a large sample of countries. The results support the value version of the HOV-model, especially in the case of developing countries.