In climate change studies the carbon cycle with its crucial component the terrestrial biosphere is of great importance due to the ability of the biosphere to store environmentally harmful carbon dioxide. Radar sensors, especially SAR, can here provide a useful tool for quantifying and monitoring the biosphere. Hence, the relationship between biomass and radar backscatter responses has been studied in detail in recent decades. Results show that the sensitivity of measured radar backscatter coefficient decreases with increasing amount or density of present biomass. In the so-called saturation region, the radar backscatter saturates at a biomass depending on the employed wavelength. While for higher frequency bands like C-band (3.95-5.8 GHz), biomass can be measured up to ~50 ton/ha, the amount of measurable biomass increases with decreasing frequency (due to the increasing wavelength), such that at L-band (1-2.6 GHz) ~ 100 ton/ha and at P-band (0.23-1 GHz) ~200 ton/ha biomass can be measured. Further, the sensitivity of radar to biomass is different for co- or cross-polarized backscatter since the level of saturation depends not only on frequency but also on vegetation (e.g., height, structure, density, moisture) and soil surface (e.g., roughness, moisture) parameters. Overall, the saturation of radar backscatter depending on biomass has to be considered when analyzing SAR data.