I acknowledge with gratitude the support that I received for my research during 1999/2000, when I held a fellowship at the International Center for Economic Research (ICER, Turin), as well as the continuous support that I received from the Institut pour le Management de la Recherche et de l?Innovation (IMRI) at the University Paris Dauphine. I am particularly grateful to Valérie Fleurette and Stephanie Pitoun. In the course of the preparation of this book, I enjoyed many stimulating discussions with a number of friends and colleagues. I am particularly grateful to my colleagues Maurice Cassier, Robin Cowan, Paul David, Jacques Mairesse, Ed Steinmueller, and Eric von Hippel for great discussions, detailed suggestions, and challenging exchanges. Many other friends and colleagues have been involved at various stages of the preparation of this book. They all have contributed to make the writing of this book an enjoyable and memorable enterprise. Warm thanks to Norbert Alter, Cristiano Antonelli, Rémi Barré, Eric Brousseau, Michel Callon, Uwe Cantner, Ann Carter, Iain Cockburn, Patrick Cohendet, Jean-Michel Dalle, Albert David, Louise Earl, David Encaoua, Emmanuelle Fauchart, Maryann Feldman, Chris Freeman, Pierre Garrouste, Fred Gault, Arnulf Gruebler, Dominique Guellec, Bronwyn Hall, David Hargreaves, Armand Hatchuel, Liliane Hilaire Perez, Ali Kazancigil, Max Keilbach, John King, Alice Lam, Patrick Llerena, Bengt Ake Lundvall, Franco Malerba, Frieder Meyer Krahmer, David Mowery, Richard Nelson, Francis-Luc Perret, Luc Soete, Kevin Styroh, Peter Swann, Morris Teubal, Manuel Trajtenberg, Xavier Vence, Jean Benoît Zimmerman, and Ehud Zuscovitch.