Quantitative remote sensing is becoming increasingly important due to the broader availability of well-calibrated airborne and spaceborne imaging spectrometers. We demonstrate the additional benefit of imaging spectrometers in the retrieval of biochemical and –biophysical variables using a general overview of recent contributions of these instruments in a programmatic context and describe in detail in a regional test case the inversion of a radiative transfer model to achieve the overall goal. Imaging spectroscopy today enables the biogeophysical and biogeochemical variables of the continental biosphere processes to be measured with calibrated physical units and quantifiable accuracy. During a large field experiment in the Swiss National Park in 2002, DAIS 7915 and ROSIS imaging spectrometer flights were carried out simultaneously with ground measurements. We constrain the inversion of a radiative transfer model (GeoSAIL) to retrieve parameters such as LAI, fractional cover, dry matter, and water content. We demonstrate that the retrievals are performed with high accuracy and conclude that the derived canopy variables represent the actual spatial distribution of forest biophysical and biochemical properties as they occur in the landscape.