Climate protection activities must, according to the Kyoto Protocol, satisfy the criterion of "Additionality", in order to be recognised as Clean Development Mechanism (CDM) Projects. But what does "Additionally" really mean? How can this criterion be put into operational practice? How can one determine wether or not a project would have been carried out without the support of the CDM incentives? The author adresses these and other thought-provoking questions, with particular focus on the application of the barrier test in Brazilian CDM projects pertaining to the Renewable Energy Sector.