This presentation of some recent advances in growth theory is motivated by two considerations. First, the works addressed by the book have not received uniform treatment in standard references. It presents a self-contained development of the subject matter including an exposition of the basic mathematics needed to study the subject. At the same time the different concepts are presented with reference to a common platform. Since economics students are exposed to the tools of supply and demand starting from the most elementary of courses, it is expected that they will readily grasp the message of modern growth theory when presented in this familiar language.A second consideration is the emphasis the book accords to the role played by externalities as in the case of most public goods where technological changes generate non-internalisable externalities which constitute one of the primary reasons for the failure of the competitive market system. The failures lead to a natural quest for policies to sustain efficient solutions with minimal interventions by the government.