The development of renewable energy sources is expected to play an important role in the implementation of greenhouse gas (GHG) reduction targets in the EU member states. Among the highly relevant instruments for promoting the renewable development is the establishment of a market for tradable green certificates (TGCs) and markets based on TGCs or equivalent instruments are already established a number of places, among these Australia, Holland, England, Italy and Texas. Other countries are in the preparation phase. Sweden and Belgium (Flanders) are moving fast towards certificate-schemes, while although an early mover the Danish Parliament has postponed the introduction in Denmark until 2004-2005. The initiatives for establishing national TGC-markets are very much in line with the fixed targets for renewable development launched by the EU-commission. Thus, although the different countries have not chosen the same concept for establishing national TGC-markets, nevertheless there seems to be a good starting point for establishing an international one. This paper discusses the separate introduction of an international tradable green certificate market into a liberalised power market, especially in relation to cost-effectiveness and the possible contributions to national GHG-reduction strategies. The combination of a TGC and a liberalised power market encounters a number of problems in relation to achieving national GHG-reduction targets. One of the main results from a three-country case study described in the paper is that those Countries most ambitious in renewable target setting by increasing their TGC-quotas will only partly be gaining the CO2-reduction benefits themselves. How large a share they gain themselves will depend only on the marginal conditions at the spot market.