The terahertz region is between the optical wave and the so-called microwaves; it had not been studied until 1963, when Nishizawa started the development of a THz wave generation based on the character of lattice or molecular vibrations. In 1979, Raman laser oscillation was realized using GaP, and in 1983, the oscillation of lattice vibration (12 THz) was achieved by mixing with the original wave. Recently, many kinds of oscillators have been developed: LiNbO3 and others for parametric oscillations, TUNNETT diode, so-called Ballistic SIT, etc. These frequencies can induce lattice or molecular vibrations, observable through reflection or transmission. Therefore, terahertz technology is useful for detection of toxins, including bacteria and viruses. It can be applied for investigation of structural changes in molecules, including those caused by disease or medical treatment. At the same time, it can heat up selectively a specified structure of a polymer and, hence, may be used for thermal treatment, or to enhance the reaction with a specific structure, suppressing side effects.