Several models are presented in which factor mobility leads to an increase in the volume of world trade. The models share the common characteristic that the basis for trade is something other than differences in relative factor endowments. These alternative bases for trade include returns to scale, imperfect competition, production and factor taxes, and differences in production technology. Taken together, the models suggest a more general idea: the widely held notion that trade in goods and factors are substitutes is in fact a rather special result which is a general characteristic only of factor proportions models.