Wetlands comprise 14% of the land area of Canada. They have considerable impact on water storage and runoff, water quality, atmospheric exchanges of carbon, and important elements such as nitrogen. In less remote parts of Canada, wetlands have suffered from reclamation, exploitation, contamination and degradation, which have seriously impaired their ecological function. Public recognition of their environmental significance has highlighted the need for a better understanding of the hydrological processes, to better plan and manage wetland areas, restore degraded systems, and predict responses to global change. This paper reviews current hydrological research in all types of Canadian wetlands. The scope of hydrological processes discussed herein includes runoff, surface and groundwater flows, evaporation, microclimate, water balance, geochemical and solute transport phenomenon, carbon dynamics, isotope studies, exploitation and restoration. Field, laboratory and modelling studies are included. Copyright © 2000 John Wiley & Sons, Ltd.