Budget negotiations are considered to be economically rational and interest-based processes. Therefore, the question what negotiations of the Multiannual Financial Framework (MFF) 2021–2027 really mean for theories of European integration seems to call for a short and simple answer: rational choice approaches, might they be institutionalist or liberal intergovernmentalist should best explain EU budget negotiations. However, under closer empirical scrutiny, the MFF negotiations for the EU's 2021–2027 budget show signs of both path dependency, innovation as well as the influence of cognitive frames, which question a purely cost-benefit reading of the process. This chapter argues that these elements question a theoretical understanding of MFF negotiations as processes purely based on cost-benefit calculations. While these calculations definitely exist – and hence rational choice approaches offer useful starting points in our understanding of the process – combining the influence of strategic cost-benefit thinking with the influence of specific cognitive frames provide a better framework for explaining both the process and the outcomes of European MFF negotiations.