Amidst debates between the North and the South, Emission Trading (ET), Clean Development Mechanism (CDM), and Joint Implementation (JI) were adopted as flexible mechanisms under the Kyoto Protocol. These mechanisms allow developed countries to meet their emission reduction targets by investing in clean projects in other countries of their choice. The implementation of these mechanisms have however been faced with many problems which cast doubts on their efficacy as viable options for combating climate change. One main criticism of these mechanisms is that they lead to a trade off between sustainability and emission reduction. This paper examines the efficiency of these mechanisms in combating climate change. It reviews the main criticisms of the flexibility mechanisms in an attempt to answer the question whether the flexibility idea should still be retained as part of the post 2012 commitments. While arguing in favor of flexibility, this paper offers ideas on how their effectiveness can be enhanced in the post 2012 commitment period.