The use of acoustic technology is not new. The first acoustic systems for aircraft and submarine detection were built during World War I. Over the last few years and with the advance of computing, memory storage efficiency, and programming, signal processing techniques have advanced significantly. As a result, acoustic capabilities have become more attractive in maritime and border security. They can now be applied to detect targets of interest at longer distances at low false alarm rates, better classification, and tracking. This book describes the principles of acoustic waves, signal processing techniques, and current and future applications of acoustic technology for port and border protection.