The article examines the on-going negotiation process towards a post-2012 climate change agreement in the light of the principle of common but differentiated responsibility (CBDR). The said principle is often identified as the cornerstone upon which State commitments are to be built. Nevertheless, the diversity of views as to how the CBDR principle should actually be put into operation in the new agreement is rather discomforting. The article reviews the negotiation work carried out in this respect and maps out the way that CBDR has been treated in the process.