The purpose of this volume is to analyze the microfoundations of knowledge spillovers. The microeconomic analysis of spillovers leads to the insight that the spillover and flow of knowledge is not at all automatic. Instead, this volume suggests that a filter exists between knowledge and its economic application. The focus of this volume is on several key mechanisms that serve to reduce this filter and facilitate the flow of knowledge. In particular, the volume draws on an emerging literature identifying the role of knowledge spillovers to investigate significance of labor mobility and informal networks as mechanisms facilitating the flow of knowledge. No field in economics has dealt extensively with the microeconomics of knowledge spillovers. This volume brings together scholars from a broad spectrum of fields including labor economics, regional economics, the economics of innovation and technological change, and sociology to introduce new insights yielded from the microfoundations of knowledge spillovers.