The Marcell Experimental Forest (MEF) in northern Minnesota, USA may be the longest running research and monitoring program on the hydrology of peatland catchments. The MEF sits astride a continental divide where the headwaters of the Mississippi, St. Lawrence, and Hudson Bay adjoin. When established in 1961, the MEF, with little topographic relief and large fractions of watersheds in peatlands, was distinct from the steep, mountainous catchments that typified other research catchments of the USDA Forest Service. This terrain and the presence of peatlands are representative of vast areas of the Northern Hemisphere, and the research program fills an important role in environmental monitoring and research in hydrology, ecology, biogeochemistry, and environmental change. During the 1960s, six research catchments were established and hydrological, meteorological, and water chemistry monitoring were initiated. Since then, the research and collaborations have proliferated to include new monitoring and ecosystem manipulations, with several paired-watershed studies, that allow the assessment of land management and environmental change effects on forests, water availability, and biogeochemical cycles. Research at the MEF remains vibrant, especially now that the site hosts a large-scale climate manipulation study (the SPRUCE Experiment). Herein, we present information on the site, contacts, long-term monitoring, experiments, and key findings.