The Clean Development Mechanism (CDM) has been a great success in promoting mitigation projects in developing countries in the past several years. However, for various reasons, there have also been many calls for reform of the CDM. The international community has agreed that the CDM should continue and could be improved, but has not reached an agreement on the way forward. One of the issues under intensive debate is whether to create new market mechanisms, namely sectoral mechanisms. Regardless of what future agreement on this aspect would be, both lessons from the CDM practice and issues related to the operationalization of the possible new mechanisms should be fully taken into consideration. One possible solution could be developing a flexible system that suits the different situations in different countries and/or sectors.