The research project JETSET focused on emissions trading as an instrument of environmental regulation in the European context in an interdisciplinary manner. In the first project phase four basis projects were developed which highlighted various aspects of emissions trading from a disciplinary perspective: Emissions trading systems and the building of institutions, Risk and market power, Social discourse and social perceptions as well as Land use and Energy. Here, the ZEW analysed the behaviour of market participants of emissions trading systems with incomplete information and imperfect competition. In the second phase, from 2005 on the project group developed four integrated cross-section projects that investigated scenarios of an international linkage of the EU Emissions Trading System: Policy scenarios, Enlargement and climate targets, Economic and emission impacts and Institutional and procedural aspects of linking emissions trading systems. Employing numerical simulation models, the ZEW analysed the economic and emission effects of linking the European Emissions Trading System internationally as well as the use of the project-based mechanisms of the Kyoto Protocol (Clean Development Mechanism and Joint Implementation) by EU member states. The model simulations by ZEW show that linking the current EU system internationally would generate only minor cost savings. A stricter allowance allocation to the covered installations could however boost the economic prospects of linking the EU Emissions Trading System in the future. For further information please visit the project homepage.