The Physikalisch Meteorologisches Observatorium Davos (PMOD) has been studying the influence of solar radiation on the Earth’s climate. In 1926, the Observatory joined the Swiss Research Institute for High Altitude Climate and Medicine Davos and has since become part of this foundation. At the request of the World Meteorological Organization (WMO), the Federal Council decided in 1970 to finance a calibration center for radiation measurement as Switzerland’s contribution to the World Weather Monitoring Program of the WMO. Following this decision, the PMOD was commissioned to establish and operate the World Radiation Center (WRC)The World Radiation Center maintains the primary standard for solar irradiance consisting of a group of high-precision absolute radiometers. In response to further inquiries from the WMO, a calibration center for atmospheric longwave radiation measuring instruments was established in 2004, and in 2008 the calibration center for spectral radiance measurements to determine atmospheric turbidity. Since 2013, the European UV calibration center has also been operated by the World Radiation Center.The PMOD/WRC develops and builds radiometers that are among the most accurate of their kind in the world and are used both on the ground and in space. These instruments are also available for purchase and have long been used by Meteorological Services worldwide. In addition, a global network of atmospheric turbidity monitoring stations is equipped with precision filter radiometers developed by PMOD/WRC.Data collected in space and by means of ground measurements are analyzed in research projects on climate change and solar physics. This research activity is integrated into national (in particular with ETH Zurich) and international projects.