The discussion paper, prepared in the context of the Carbon Market Mechanisms Working Group, discusses how transparency of Article 6 cooperation can be ensured. More specifically, it discusses optimisation options of the envisioned operationalisation of accounting, reporting and review processes under Article 6 and their links to reporting and review processes under the enhanced transparency framework of Article 13. Building on the Article 6.2 and 6.4 negotiation draft texts and the recent developments at informal discussions in June and September 2021, the authors derive concrete recommendations to refine the provisions at the 26^th Conference of the Parties.