This is the first of a proposed series of Special Issues of Hydrological Sciences Journal meant to give state-of-the-art overviews of the sciences covered in the different Commissions and Committees of the International Association of Hydrological Sciences (IAHS). The International Committee for Remote Sensing and Data Transmission (ICRSDT) organized this first Special Issue to cover the current research in and operational applications of remote sensing technology in hydrology. The latter applications are becoming more important because remote sensing techniques have the ability: (a) to measure spatial, spectral and temporal information; and (b) to provide data on the state of the Earth's surface. It is also a rapidly changing domain with new sensors, platforms and application techniques being developed to give hydrologists new data and new views of the landscape with which to evaluate the Earth's surface
(Rango, 1994; Running etal., 1994). Remote sensing provides observations of changes in hydrological states and variables over both time and space that can be used to monitor hydrological conditions and changes.