Watersheds are under increasing pressure worldwide, as expanding human activities coupled with global climate change threaten the water security of people downstream. In response, some communities have initiated investments in watershed services (IWS), a general term for policy-finance mechanisms that mitigate diverse watershed threats and promote ecosystem-based adaptation. Here, we explore the potential for increasing the uptake and impact of IWS, evaluating what limits its application and how institutional, financial, and informational barriers can be overcome. Our analysis complements the growing literature on individual programs by identifying levers at regional and global scales. We conclude that mainstreaming IWS as a cost-effective strategy alongside engineered approaches will require advances that (i) lower institutional barriers to implementation and participation in IWS; (ii) introduce structural market changes and standards of practice that account for the value of watersheds’ natural capital; (iii) develop practical tools and metrics of IWS costs and benefits; and (iv) share success stories of replicable institutional and financial models applied in varied contexts.