The study of international firm activities forms a very active sub-field of international economics with direct implications for economic policy. In this literature, micro-econometric investigations using longitudinal data at the firm level and micro-economic modelling of heterogeneous firms that are involved in various forms of international activities mutually fertilize each other (see the surveys by Greenaway and Kneller (2007), Helpman (2006), López (2005), and Wagner (2007)). Members of The International Study Group on Exports and Productivit