The belief according to which supply factors are especially important in the developing world, whereas demand management might be more relevant in already advanced economies is too simplistic to be of any practical utility. Each economy has its own structure (its own history) and this chapter is devoted to the analysis of the different structural constraints that may slow the growth and development process of specific countries. In some cases, the constraint may come from some supply bottlenecks (excessive concentration of land ownership, insufficient access to credit, etc.); in other cases, it might happen that households, the government and the business sector do not spend enough to exploit the productive potential of the country; in other cases, again, the economy is not fully using its installed productive capacity, but has reached the upper limit of the current account deficit, meaning that in principle an aggregate demand stimulus could work, but the economy lacks the foreign exchange needed to finance the increase in imports that such stimulus would inevitably generate; and so on and so forth. There are so many possible structural and macroeconomic constraints, and the “art” of the economist is to understand what is relevant and what is not in any specific scenario. To reach this goal, the chapter builds on the solid shoulders of M. Kalecki, one of the most brilliant, eclectic, and pragmatic scholars in the history of economic thought.