Once appropriate THz wave sources and detectors become available, researchers will be interested in developing application technologies, in order to utilize the THz waves. By far, most of the applications using THz wave can be sorted into the following two categories, namely, THz wave spectroscopy and THz wave imaging. When a pulsed THz wave is used, the mainly employed spectroscopic technique is THz wave time-domain spectroscopy. In this chapter we briefly introduce the concept of THz wave time-domain spectroscopy and THz wave imaging. Then we discuss a few spectroscopic and imaging techniques.