This book describes the theoretical development of a suite of advanced scattering models necessary for interpreting fisheries and zooplankton acoustics, before presenting state of the art data processing techniques. Systematic development of scattering models of targets with different geometric and physical properties are presented, reflecting scientific advances in scattering modeling over the past few decades. The authors hope this book can also be used as a reference or guide book for acoustic scientists to understand the underlying physics behind acoustic scattering by aquatic fauna, enabling them to process and interpret the recorded acoustic data correctly.