Open innovation is about firms' external relations with other firms and organizations. It is a topic which has attracted an immense amount of attention, but which has also been heavily criticized due to the diversity of the ideas and fuzziness of its key concepts. To date, the bulk of the literature on open innovation draws on case study material to illustrate the operation of firms in an anecdotal way. By contrast, this book examines open innovation practices by using large-scale data sets and stresses their impact on firm performance. The authors examine four key issues: differences between firms in open innovation practices, public funding to enhance external relations, R&D outsourcing of firms, and the role of human resources in R&D and innovation. The conceptual and measurement issues attached to open innovation explored in this timely book will prove essential to academics. Practitioners from large firms who are closely engaged in the practical organization of open innovation will benefit from the authors insights on outsourcing R&D and the need for the right kinds of human resources.