This module illustrates the basics oftrade policy analysis. It focuses on the followingquestions: 1) What do countries gain by trading with eachother instead of opting for self sufficiency?; 2) What arethe main instruments of trade policy?; 3) How do they affectprices, output and welfare?; and 4) What are the effects oftrade policy in the presence of market imperfections. Thisbook is arranged as follows: In Section one, the authorsshow how the main welfare effects of trade policy can beanalyzed. In Section two, the authors illustrate the mainsources of gains from trade, namely, how and whyinternational trade raises welfare. In Section three, theauthors examine the main trade policy instruments anddiscuss their welfare effects, while in Section four theauthors ask whether there is scope for trade policy in thepresence of externalities generated by domestic productionor when markets are imperfectly competitive. The main issueswill be illustrated in very simple and intuitive terms.Boxes will instead provide a more rigorous analysis of thearguments discussed in this module.