The principal aim of this book is to provide the reader with the understanding of the possibilities and features of THz identification as opposed to more traditional techniques such as X-rays, microwaves, etc. by elucidating and illustrating the principles of THz identification and its applications in a systematical way. Its scope includes a description of the physical principles of THz generation, transmission and detection, as well as of the applications of THz identification. The inherent advantages and potential benefits of the terahertz (THz) phenomenon, potential that encompasses various aspects such as THz sensing, imaging and material properties investigation with THz radiation for Defense (military) and security applications serve as an important stimulus for the interest in emerging THz science and technology, in particular, the very rapid growth of this new field. This text presents some of the leading fundamental research efforts towards the realization of practical THz devices applications for military and security applications.