This study addresses two interrelated issues in international taxation. The first objective is to assess the nature and extent of the international mobility of foreign direct investment. This empirical work is based on the operations of US multinational corporations abroad (production, employment and capital stock), not simply on financial flows of foreign affilitates. It considers whether distinctions between horizontal versus vertical integration can be applied to opertions in developed versus developing countries, and whether either form of integration is very sensitive to tax and cost conditions, not only in the host country but in the US. Growing sensitivity of foreign direct investment to taxes is one reason for governments to be concerned about tax competition among jurisdictions to attract economic activity. Tax competition, however, also arises from an attempt to shift the real activity. The second objective is to assess how tax competition is affecting the structure of national tax systems and whether efforts at international coordination of tax policy are likely to affect the progression of such changes in the future.