The lawfulness of carbon border adjustment measures (CBAMs) under general international economic law and particular economic agreements is explored; specifically, if their international lawfulness can be determined by thinking of them as countermeasures necessary to implement climate change obligations. As there are no non-discriminatory obligations under customary international law, it is argued that CBAMs are lawful under general international law, but under particular international economic agreements they can be seen as countermeasures lawfully taken in response to breaching the obligation to curb GHG emissions, allowing their justification as a breach of primary non-discriminatory economic obligations, particularly the national treatment principle under the GATT and GATS. This shifts the burden of proving necessity/proportionality to the State in breach of the obligation. CBAMs are fundamentally lawful measures and can only give rise to compensation if it they are unnecessary/disproportionate. This chapter also assesses whether they can be thought of as erga omnes contractantes obligations under international economic agreements, particularly the GATT and the GATS.