Terahertz (THz) radiation, which is electromagnetic radiation in a frequency int- val from 0.3 to 10 THz (1 mm-30 ?m wavelength), is the next frontier in science and techlogy. This band occupies a large portion of the electromagnetic sp- trum between the infrared and microwave bands. Basic research, new initiatives, and developments in advanced sensing and imaging techlogy with regard to the THz band remain unexplored compared to the relatively well-developed science and techlogy in the microwave and optical frequencies. Historically, THz techlogies were used mainly within the astromy c- munity for studying the background of cosmic far-infrared radiation, and by the laser-fusion community for the diagstics of plasmas. Since the ?rst demonstration of THz wave time-domain spectroscopy in the late 1980s, there has been a series of signi?cant advances (particularly in recent years) as more intense THz sources and higher sensitivity detectors provide new opportunities for understanding the basic science in the THz frequency range.