This technical note offers guidance and identifies options for developing baselines for scaled-up crediting programs under the Paris Agreement. Establishing baselines is partly a technical, methodological challenge, but the biggest uncertainties arise from unresolved questions regarding international rules under Article 6 of the Paris Agreement, as well as how crediting programs may interact with achievement of countries' "nationally determined contributions" (NDC). How scaled-up crediting programs should complement a host country's overall climate and sectoral policy goals, and how to coordinate baseline development — and overall crediting program design — with other aspects of national climate policy? This note has laid out some core principles that are likely to inform rules for new crediting mechanisms (i.e., environmental integrity and avoiding double counting), and presented some options and preliminary considerations for how to establish baselines in light of these principles.