This volume intends to make sense of the current 'puzzle' that international parliamentary institutions represent. Their rapid growth in numbers and under a diversity of forms in the post-Cold War emerging new order is a worldwide phenomenon, even if its first expression dates back to the end of the 19th century. Their objectives vary from creating a permanent institutional structure for the peaceful settlement of disputes to promoting transparency in international politics, including the reinforcement of civil society participation in regional integration schemes. Are these goals kept nowadays? Are they being achieved? Which means and interests define the work within these assemblies? The three parts of the book include analyses of supranational and non-supranational regional parliaments and the specific case of the inter-regional relations established by the European Parliament.