By Gisele Umbhauer ...1 Part I : Interaction and Macro-Struture : an Overview Economies with Interacting Agents By Alan P. Kinnan (GREQUAM) ...*...17 Spatial Interactions in Dynamic Decentralised Economies : a Review By Giorgio Fagiolo (EUI) ...53 Network, Interactions between Economic Agents and Irreversibilities : the Case of the Choice among Competing Technologies By Patrick Cohendet (BETA) ...93 Rationality and Heterogeneity in Stochastic Aggregation Models By Jean-Michel Dalle (IEPE) ...123 Part II : Local Interaction, Learning and Diversity Networks Competition under Local Interaction and Behavioral Learning By Nicolas Jonard (BETA), Patrick Llerena (BETA) and Babak Mehm- pazir (BETA) ...149 Can Neighborhood Protect Diversity By Gisele Umbhauer (BETA) ...167 Interaction of Local Interactions: Localized Learning and Network Exter- nalities By Nicolas Jonard (BETA) and Murat ytldlZoglu(BETA) ...189 viii List of Contribution Evolution of Cooperation with Local Interactions and Imitation By Vanessa Oltra (BETA) and Eric Schenk (BETA) ...2 05 On the Frontier: Structural Effects in a Diffusion Model based on Influence Matrixes By Alexandre Steyer (REC) and Jean-Benoit Zimmermann (GREQUAM) ...223 Part III : Behaviors, Externalities and the Emergence of Networks Networks, Specialization and Trust By Ehud Zuscovitch (BETA) ...243 Network Externalities, Cost FUnctions and Standardization By Hubert Stahn (BETA) ...265 The Emergence of Network Organizations in Processes of Technological Choice: a Viability Approach By Jean-Pierre Aubin (IIASA) and Dominique Foray (IRIS-TS) ...283 Are more Informed Agents able to shatter Information Cascades in the Lab? By Marc Willinger (BETA) and Anthony Ziegelmeyer (BETA) ...