Introduction: Structuring Informal Mechanism Of Knowledge Transfer -- Geographic and Relational Proximity -- The Spatial Distribution of Entrepreneurial Support Networks: Evidence from Semiconductor Initial Public Offerings from 1996 through 2000 -- 4 The Impact of Regional Social Networks on the Entrepreneurial Development Process -- Social Networks, Informational Complexity and Industrial Geography* -- Transnational Networks and The Evolution of the Indian Software Industry: -- The Mobility of Economic Agents as Conduits of Knowledge Spillovers -- Scientific knowledge flows and labour mobility -- Firm Placements of New PhDs: Implications for Knowledge Transfer -- Basic Research, Labour Mobility and Competitiveness -- Science-Industry Relationships in France: Entrepreneurship and Innovative Institutions -- Knowledge Creation And Flows In Science.The purpose of The Role of Labour Mobility and Informal Networks for Knowledge Transfer is to analyze the microfoundations of knowledge spillovers. The microeconomic analysis of knowledge 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 The Role of Labour Mobility 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 labour mobility and informal networks as mechanisms facilitating the flow of knowledge. No field in economics has dealt extensively with the microeconomics of knowledge spillovers. Thus, it is important to include the perspectives and insights of research approaches that span a broad spectrum of fields in economics. This work brings together scholars from labor economics, regional economics, the economics of innovation and technological change, and sociology to introduce new insights yielded from the microfoundations of knowledge spillovers.