This part of the book focuses on models of endogenous technological change Chapter 12 discusses various different approaches to technological change and provides a brief overview of some models of technological progress from the industrial organization literature Chapters 13 and 14 present at the baseline endogenous technological progress models developed by Romer, Grossman and Helpman and Aghion and Howitt Chapter 15 considers a richer class of models in which the direction of technological change, for example, which factors technological change will augment or complement, is also endogenous