How can policy analysts use empirical programme evaluation studies to perform ex-post assessments of environmentally related tax policies? A number of studies credibly identify causal effects of environmentally related tax policies, but do not necessarily provide all the information needed to fully inform the policy-making process. This chapter argues that cost-benefit analysis (CBA) could enrich ex-post assessments of environmentally related tax policies, given that CBA provides decision makers with a broader perspective of social costs and benefits and allows the identification of potential trade-offs among policy objectives. These points are developed and illustrated by reference to the initial effects caused by the French feebate programme for carbon dioxide-efficient motor vehicles after its introduction in 2008. The analysis reveals the practical relevance of considering non-climate externalities, such as local air pollution, the social cost of the fiscal revenue losses and changes in producer and consumer surplus.