Assessments of the past are essential to the struggle over the right to define the normative position of history under the UN Framework Convention on Climate Change (UNFCCC). Despite this importance, attempts to analyze the use of history in this context are rare. This thesis aims to investigate how assessments of the past are used in UNFCCC negotiations on responsibilities to act, focusing on negotiations on historical responsibilities. The research questions concern how discourse on historical responsibility: 1) can be structured, 2) is influenced by UNFCCC negotiating practice, 3) has been structured in the UNFCCC, and 4) has enabled agreement despite considerable conflict. Official UNFCCC documentation between 1991 and 2011 was studied using discourse analysis. This study suggests: first, the UNFCCC discourse on historical responsibility conveys two main assessments—a proportional and a conceptual one—of how the past could be used to differentiate responsibilities to act. Second, the strong consensus focus necessitates rationales underlying an “agreeable history” that is neither too flexible, allowing arbitrariness, nor too rigid, reducing Parties’ likelihood of ratifying. Third, as the past evolves, new situations challenge discourse that potentially engages policy makers with a need to rearticulate history. Fourth, if the context changes, so may the importance ascribed to particular assessments of the past. If the stakes increase over time, even more effort is required to reach agreement, which simultaneously becomes more important in solving problems of common concern. Fifth, power seems difficult to circumvent, even by means of cleverly designed negotiating practice. If so, multilateral environmental negotiations could increase the legitimacy of outcomes among Parties in two principal ways: first, by identifying the core conflict that drives negotiations and, second, by evaluating how multilateral environmental negotiations handle conflict. Obscuring or ignoring conflict will likely only reduce the legitimacy of the negotiations.