In general, economic decisions are made in order to maximize individual well-being or, equivalently, to maximize the returns of these decisions to the individual. However, while taking their environment as given, the decision-makers often do not explicitly take into account what consequences their decisions have on the aggregate level. Many macroeconomic phenomena can be seen as unintended or unforeseen consequences, returns, to the decisions of rational individuals. This book presents several models in this spirit. The first part investigates the role of individual education decisions for...