The field of plasmonics has generated considerable interest in recent years. This talk focuses on the applications of plasmonics in the terahertz region. THz surface plasmon based devices can be constructed using the standard techniques of semiconductor processing technology, as the characteristic length scales are commensurate with the wavelength (i.e. a fraction of a millimetre); and so this task can be easily accomplished. Emerging developments to be discussed include: sensors (including biological sensors); techniques for guiding, concentrating and manipulating THz radiation; and new methods for THz imaging and microscopy.