This book provides an extensive critical review of seismic inversion methods and applications. Hydrocarbon reservoir extensions and properties cannot be accurately defined from information provided by geological data, geophysical data, and well log data. Seismic data has adequate spatial coverage but lacks vertical resolution, while well data has excellent vertical resolution but spatially sparse. Seismic reflection amplitudes are related to pore fill and lithology changes. Seismic AVO analysis and inversion exploit variation of amplitudes with angle of incidence to derive useful attributes and elastic rock properties such as velocity, impedance, and density. Seismic inversion attempts to fill the gap between and away from the already drilled wells with rock properties that are available from the measured and/or interpreted well log data. In this endeavour, seismic data, well log data, and all available geological model data are integrated to predict rock and ultimately reservoir properties such as porosity, water saturation, shale content, brittleness, and pore pressure. This book is aimed at graduate and postgraduate students, academics, and geoscientist exploiting earth resources. It is especially directed to oil and gas industry professionals in supporting their efforts in quantitative reservoir description from seismic data. While brief theoretical derivations are provided to understand power and limitations of inversion methods used, emphasis has been on the practical applications. A comprehensive critical review of the seismic inversion and AVO theory and applications published and presented at technical meetings is provided with ample references and further references for probing geoscientists.