This book is on millimetric signal attenuation due to absorption and scattering by rain using both regional estimates of rain rate and different total cross section models with different rain DSD for various rain types in the frequency range of 10 to 100 GHz. The Method of Moments is applied to obtain the DSD models and different extinction coefficients are used for the computation of specific rain attenuation. Theoretical results obtained are then compared with the proposed models as well as other known models for both vertical and horizontal polarization for the various rain rates. Measured and calculated rain attenuation obtained using the Pruppacher-Pitter technique and the Mie Scattering technique are also presented. Incorporation of available DSD data and measured rain rate with the derived scattering amplitude coefficients is then done to estimate the total and specific rain attenuation for the South African region. The depolarization effects on radio signals due to the physical properties of raindrops such as shape, size distribution, refractive index, and canting angle are also addressed.