The open economy and the effects of economic policy - an introduction; tariffs in a Mundellian-Keynesian model; output, the exchange rate and quotas; commercial policy, capital mobility in the fixed price model with a money sector; tariffs under capital mobility and rational expectations; commercial policy and the portfolio model; commercial policy, government stabilization policy, output and employment under rigid real wages; commercial, monetary and fiscal policy in a dynamic macromodel with flexible prices and wages.