Many Parties to the Paris Agreement have expressed greenhouse gas mitigation targets relative to a baseline scenario, or “baseline targets”. Baseline targets in nationally determined contributions (NDCs) could potentially change over time including to update assumptions of emission drivers or reflect improved methodologies. This paper examines issues that can arise under Articles 4 and 6 of the Agreement when baseline targets are updated, such as potential implications of using consistent methodologies throughout the NDC implementation period. The paper also examines transparency-related issues, e.g. information needed for accounting that would be reported and reviewed under Article 13 of the Agreement. Past baseline and reference scenario reporting experience highlights relevant lessons for accounting for baseline targets, including on transparent reporting of baseline scenarios. The paper identifies reporting and accounting guidance options, including when certain types of updates could be applied to baseline targets, that could help Parties address some of these issues.