The usage of Earth reflected signals from Global Navigation Satellite Systems (GNSS) for remote sensing of water, ice/snow and land surfaces is a recent hot topic of geoscientific and GNSS research (GNSS-Reflectometry, GNSS-R) with numerous intense international scientific activities. Standard geodetic receivers of global and regional ground networks are used to operationally derive information on soil moisture, vegetation, snow properties, and water levels near the GNSS antennas of existing or dedicated ground networks. Specific receivers on the Earth’s surface and aboard flight platforms including satellites are applied to monitor, e.g., sea surface heights or wind speed/directions of water surfaces, key applications with respect to climate change characterization and natural hazard monitoring. Several GNSS-R satellite missions were recently launched, or are in preparation (e.g., TechDemoSat-1, CYGNSS, GEROS-ISS, G-TERN), which provide observations on a global scale. The history of GNSS-Reflectometry for Earth Observation is briefly reviewed and selected results for various geoscientific applications are given to illustrate the versatility of the GNSS-R method. Future prospects of the method are discussed taking into account current and potential future links to the IGS activities.