This short paper provides the framework and introduction to this special issue of International Journal of Wildland Fire. Its eight papers were selected from those presented at two consecutive conferences held in 2018 in Europe and the USA that focussed on the impacts of wildfire on factors that regulate streamflow, water quality, sediment transport, and aquatic habitats. Despite decades of watershed research, our understanding of the effects of wildfires on the processes that regulate clean water supply remains limited. Here, we summarise the key challenges and research needs in this interdisciplinary field and evaluate the contributions the eight special issue papers make to improved understanding of wildfire impacts on watershed processes. We also outline research priorities aimed at improving our ability to predict and, where necessary, mitigate wildfire impacts on watersheds. Achieving these advances is all the more pressing given the increasing extent and severity of wildfires in many areas that are the source of clean water for major population centres.