This introduction presents an overview of key concepts discussed in the subsequent chapters of this book. The book provides an overview of how radars operate, discusses various types of radar waveforms, and highlights several indoor radar applications. It deals with multiantenna radar systems for indoor human monitoring. The book reviews basics of radar and the radar range equation and describes the essence of pulse-Doppler radar. It also reviews the fundamentals of Frequency-modulated continuous-waves (FMCW) and stepped frequency continuous-waves (SFCW) radars and their use in indoor radar applications. The book overviews signal processing and target detection techniques, and highlights their utilization in various indoor radar applications. It describes the basics of image formation in indoor radar and discusses various civilian and military applications of indoor radar with a focus on through-the-wall radar (TWR), assisted living radar, and concealed weapon detection.