The introduction outlines how international economic institutions increasingly are involved in climate politics, why this involvement matters and why it makes sense to describe it in terms of economisation. Specifically, the chapter outlines the concept of economisation and how it consists of framing an issue as an economic issue as well as enabling economic institutions to address the issue. The book uses economisation to understand the G20, OECD and IMF’s respective output regarding fossil fuel subsidies and climate finance respectively, as well as the factors that shape this output and the consequences of the output at the international and domestic levels. Subsequently, the chapter outlines the relevant literature on climate governance and international institutions/organisations, and identifies the contribution of the book to these bodies of literature. Next, the chapter explains why it makes sense to select the cases of climate finance and fossil fuel subsidies, which are both characterised by economic institution involvement, while the relationship between their impact on state budgets and on the environment pulls in opposite directions. The section proceeds with why the selection of the G20, OECD and IMF is academically relevant. The following section outlines the use of data sources and methods in the analysis.