In this book we intend to discuss economic fluctuations and growth and possible stabilizing fiscal policies. Since these topics are major preoccupa tions of economic theorists and have been extensively discussed since the classics, one may wonder why another book on these subjects. A possible defense is that we are going to do so in the framework of a two-sector model where the main featureS of each sector depend on the characteristics of the goods produced by the sector itself. The conventional wisdom suggests that the problem of (dis )aggregation in growth and business cycle theory is...