The terahertz region of the electromagnetic spectrum is typically defined in the frequency range 100 GHz to 10 THz, corresponding to a wavelength range of 3 mm to 30 microns. The millimetre wave region lies between 30 GHz and 300 GHz, corresponding to a wavelength range of 10 cm to 1 mm and overlaps a portion of the terahertz region. Following the development of coherent sources and detectors in the early eighties, there has been growing interest in the role of terahertz technology for security and defence. The terahertz region offers a huge expanse of unused bandwidth, which currently presents a significant advantage for both security and defense initiatives. The ability of terahertz radiation to probe intermolecular interactions, large amplitude vibrations and rotational modes, in addition to showing polarization sensitivity makes terahertz radiation a unique and diverse region of the electromagnetic spectrum. The additional ability of both terahertz and millimeter wave radiation to 'see through' common materials, such as thick smoke, fog and dust, which are often considered as opaque in other regions of the electromagnetic spectrum offers further advantages over other optical techniques. Due to the heavy attenuation of terahertz radiation by water vapour, millimeter wave technology is more suited for long range, all-weather imaging systems, whereas terahertz technology has more potential for high resolution short range imaging and spectroscopy. The potential of terahertz and millimetre wave technology and their associated potential for port and harbour security initiatives are discussed.