The twenty-two papers collected in this volume illustrate the itinerary of Henry Tulkens, an applied theorist, on the occasion of his retirement from teaching. The collection is structured in four parts: I. Decentralized resource allocation processes for public and private goods - II. Environment, public goods and externalities - III. Efficiency analysis - IV. Fiscal competition and optimality. The four pictures above evoke a key concept, method or model used in each of these four parts: MDP-type processes to determine feasible paths to efficiency and coalitional stability - CLIMNEG World Simulation model to explore alternative environmental scenarios for the planet - Free Disposal Hull efficiency analysis to drop convexity and help deal with outliers - Non Cooperative Fiscal Equilibria to characterize the outcomes of fiscal competition.