Remote sensing provides an unmatched data source for obtaining information about earth resources. This paper briefly describes the development of remote sensing, then discusses the physical and technological basis for obtaining earth resources information from airborne and spaceborne sensors. It points out that information may be derived from analyzing the spectral, spatial, and temporal variations of energy emanating from the earth's surface. The two types of analysis, image-oriented and numerical-oriented, are discussed with emphasis on the latter and machine-processing of data. Finally, applications of remote sensing technology are discussed.