Aquifer thermal energy storage (ATES) represents a promising solution for heating and cooling, offering lower greenhouse gas emissions and primary energy consumption than conventional technologies. Despite these benefits and the widespread availability of suitable aquifers, ATES has yet to see widespread utilisation, with uptake highly concentrated in select countries (Netherlands, Belgium, Sweden and Denmark). Beyond technical and hydrogeological feasibility, appropriate national policies are paramount in driving ATES deployment. This study provides an international comparison of ATES policies, highlighting best practices and revealing where measures are missing. It sources insights from a survey of experts across academia, industry and governmental bodies in 30 countries, complemented by semi-structured expert interviews. The study reveals significant differences in the existence and strength of supportive policy environments between countries with different ATES market maturity. A mere 33% of all survey respondents stated that there are policies designed to support ATES utilisation in their respective countries, while the existence of laws and regulations governing ATES was confirmed by 56% of the respondents. The interviews provide details on creating supportive environments (e.g. through facilitators like pre-existing groundwater technology use and building energy efficiency standards) and further barriers to ATES deployment. Ten recommendations for ATES policies are derived to address the following areas: legislative and regulatory issues, raising public awareness, ATES’ role in local energy transitions, and social engagement. This work aims to steer global policy towards better harnessing the potential of ATES to decarbonise buildings.