This book focuses on biomedical applications of terahertz (THz) waves. THz waves offer advantages due to their low energy (greater safety), long wavelength (less scattering), and sensitivity to water molecules. The book explores the use of THz spectroscopy in elucidating biological behaviors as well as the development of THz wave medical techniques, such as skin drug absorption imaging and cancer diagnosis. It also includes an overview of THz technology, encompassing generation, detection, and imaging methods.