The Hydropower Sustainability Tools (HSTs) are a suite of assessment tools and guidance documents developed by a multi-stakeholder forum, aimed at driving continuous improvement in hydropower development and operations. They are useful beyond their original purpose as audit tools and can be used in World Bank Group (WBG) client countries to build capacity for sustainable hydropower. The environmental, social, and governance topics addressed by the HSTs are deliberately aligned with WBG frameworks, which provides opportunities for the tools to be used as complements to World Bank Group standards, including to help clients meet WBG requirements and support WBG staff in their due diligence and supervision. It is, however, important that WBG staff should give careful thought to selecting the tool that is most appropriate, given the nature and status of a project, and in a way that is consistent with policy requirements. The tools can also be used voluntarily by WBG client countries in the absence of WBG financing. The HSTs are widely regarded as useful reference tools and recognized as the best currently available measuring stick for principles of sustainable hydropower.