For a number of years, the main EU policy response to concerns about carbon leakage. i.e. the relocation of production to jurisdictions with more lax climate policies, was to maintain a large proportion of free allowances under the EU Emissions Trading System. But another possible response has taken the form of a carbon border adjustment mechanism (CBAM). This chapter explores why the CBAM option gained such prominence from 2019 in particular, culminating in a formal proposal tabled in mid-2021. It identifies France as a consistent advocate of the idea. Furthermore, the appointment of the von der Leyen-led Commission in 2019 and the advent of the European Green Deal constituted a central turning point, although von der Leyen’s support of the CBAM idea appears to a large degree a response to European Parliament pressure. The chapter also discusses central dynamics in the decision-making process and prospects ahead, which are rendered more uncertain by the Russian invasion of Ukraine in May 2022.