Krycklan Catchment Study (KCS) is the most instrumented and well-studied meso-scale catchment in the boreal region. The 70 km2 KCS builds on three decades of catchment science that grew up around the Svartberget field station and is currently one of the most ambitious projects integrating water quality, hydrology, and aquatic ecology in running waters in the north. At present, KCS includes 18 intensively instrumented and continuously monitored sub-catchments, an extensive soil sampling program, comprehensive lake carbon-balance studies, several long-term field experiments, and a large set of ancillary data. To date, close to 20,000 stream and soil water samples have been collected (with duplicate sample archived in freezer) and analyzed providing approximately 10 million unique water chemistry observations. At the center of the catchment the 150 m ICOS (pan-European Integrated Carbon Observatory System) research tower is placed for measuring exchange of energy, water and carbon that will allow for one of the best assessments of full carbon balance at a landscape scale that presently exists anywhere in the world. At presently over 100 research projects are being conducted involvning several hundered researchers from all over the world.