In this paper we study the welfare improvement effects of international institutions which represent a system of rules used to execute international cooperation. We show that international institutions can improve welfare in the case of providing international public goods and regulating cross-border externality (CBE). This paper consists of two parts. In the first part we study the welfare-improving effects of international cooperation to provide international public goods. Two criteria are used to classify international public goods and analyse the welfare improvement effects of international cooperation: (a) inclusiveness/exclusiveness and (b) crowding/no crowding. In the second part we study the welfare improvement effect of international cooperation to regulate CBE. Two criteria are used to classify cross-border externalities for a detail analysis: (a) impacts of CBE and (b) two groups of countries, i.e. initial (player) country and other (players) countries.