The principle of common, but differentiated, responsibilities and respective capabilities (CBDR&RC) is fundamental to the UNFCCC. Some options for a nuanced model of differentiation that addresses both responsibility and capability in a changing world are explored, such as new categories of countries, and some of the political issues that such a model might face are considered. The strengths and limitations of options for graduation based on 'objective' criteria such that countries could move between categories or 'graduate' - an option provided by the UNFCCC - are discussed. Countries could also choose to join another club (e.g. the G20), self-elect into categories or differentiate among themselves implicitly by accepting different commitments and actions. CBDR&RC will form part of the overall legally binding agreement, and must apply symmetry in some respects and differentiation in others to the commitments and actions contained therein. Some possible characteristics of CBDR&RC of relevance in a regime 'applicable to all' are outlined. These include promoting climate action and using mechanisms available in the UNFCCC to instil dynamism. Differentiation on mitigation must consider the distinctions between absolute and relative reductions, as well as commitments to outcomes and implementation. CBDR&RC should be applied to mitigation, adaptation, and the means of implementation. <bold>Policy relevance</bold> In Durban, Parties agreed to negotiate a regime 'applicable to all', which sent a political signal that there should be greater symmetry between nations. The world has changed since the UNFCCC was negotiated in 1992. It is now less helpful to think only in terms of two groups of countries (e.g. Annex I and non-Annex I), and evident that there are significant differences between member states. This requires a more nuanced interpretation of the principles of equity and CBDR&RC, which is an integral part of the UNFCCC. The options for the different approaches outlined in this article might help in the construction of a more nuanced model. All must do more, while some must do more still than others. To achieve this, some defining characteristics of CBDR&RC in a regime applicable to all are suggested.
