Terahertz radiation, which fills the gap between 100 GHz and 10 THz ( = 30 µm – 3 mm) in the electro-magnetic spectrum, has seldom been used outside of astronomy and other scientific research. However, in recent years there has been a significant interest in investigating THz radiation for different new applications. Especially the ability of terahertz radiation to penetrate deep into many organic materials without the damage associated with ionizing radiation such as X-rays lead to recent interests chiefly in the fields of security technology and biomedical imaging. The attribute of many different materials to be transparent for terahertz radiation, was also the reason for many difficulties in practical applications outside of research. Using radiation that can pass through so many materials so well makes detection difficult. In addition, sources to generate light at terahertz frequencies have suffered from low output intensity and other problems. Since the 1990s, technical breakthroughs in sources and detectors have brought terahertz technology within striking distance of significant commercial markets . The pressure to develop new terahertz sources arose from two dramatically different groups - ultrafast timedomain spectroscopists who wanted to work with longer wavelengths, and long wavelength radio astronomers who wanted to work with shorter wavelengths. Today there are continuous-wave (CW) sources available as well as pulsed sources . The aim of this paper is to provide an overview of key scientific developments which currently represent the basics of the mentioned THz technology. Beginning with the working principle of opto-electronic THz sources and detectors, the paper explains different setups for transmitting and using THz radiation. Furthermore it shows different applications of different business branches and gives an outlook for industrial application in the fields of metrology and quality control.