SITES (Swedish Infrastructure for Ecosystem Science) is a national infrastructure that facilitates long-term, world-class field based ecosystem research by offering a unique infrastructure and expertise to the Swedish and international research community. SITES aims to promote high-quality research through long-term field measurements and field experiments, and by making data available. The core of SITES is nine field research stations that represent a variety of Swedish climate zones and ecosystems, including agricultural land, forests, wetlands, lakes and streams. SITES three thematic programs: Aquanet, Water and Spectral, offer open data from long-term monitoring and experimental installations. Principals of SITES are University of Gothenburg, Swedish Polar Research Secretariat, Swedish University of Agricultural Sciences (SLU) and Stockholm University. SITES is funded by the Swedish Research Council, together with the principals of the research stations. The coordinator of SITES is the Swedish University of Agricultural Sciences, where also the secretariat is located. The collaboration is regulated by a consortium agreement between the principals. SITES is governed by an independent steering group and the daily work is led by a scientifically well merited director.