To us in the twenty-first century, a growing economy is the norm. It was not always so. In the last chapter, we investigated the problem of aggregate supply: What determines the level of GDP produced? In this chapter, we use that analysis to ask the question: what makes GDP grow over time? Our analysis allows us to address questions like: Is it more factor inputs or using them better (technological progress) that explains the growth of the economy? How fast can the economy hope to grow in the long run? What effect will growth have on personal incomes? What factors promote or retard growth? Why have some economies grown rapidly and others stagnated?