Spectroscopy was first used in 1814 by Joseph von Fraunhofer as a scientific method for discovery, and to develop and test scientific hypotheses. From this beginning, spectroscopy evolved to a broadly used analytical tool for both science and applications. In the 1970’s, technology began to enable a class of instruments that measure spectra for every point in an image. The first airborne imaging spectrometer developed at the Jet Propulsion Laboratory flew in 1982. Subsequently, a wide range of imaging spectrometers have been developed, many at the Jet Propulsion Laboratory, for airborne and space platforms and they have participated in NASA mission throughout the solar system. A key lesson over this time period has been the broad applicability of imaging spectrometers to pursue a range of science and application objectives wherever there is relevant signal in the spectral range from the ultra violet to the thermal infrared. As with all optical imaging instruments, imaging spectrometers have spectral, radiometric and spatial characteristics and related requirements. Of these, uniformity, radiometric precision, and calibration have been identified as critically important for the science and application utility of imaging spectrometer instruments. These key requirements are enabling for the most advanced imaging spectrometer algorithms that retrieve parameters with units and quantifiable uncertainties. The current trend in imaging spectrometer instrumentation is for broader spectral coverage and wider swath while improving uniformity, precision, and calibration. A companion emphasis is for lower mass, power and volume, with instruments taking advantage of the latest detector, optical, electronics and computational technologies. The number of imaging spectrometers in use is increasing every year and this trend is on track to continue.