This paper describes progress in gigahertz-clocked quantum key distribution systems. It details current advances in both point-to-point and network applications. We will discuss possibilities for practical quantum key distribution using single-photon sources, and discuss the experimental system performance of GHz-clocked quantum key distribution systems focusing on issues of quantum bit error rate, net bit rate and transmission distance with different detector structures, concentrating on single-photon avalanche diode detectors, but also examining superconducting nanowire-based structures. The quantum key distribution system is designed to be environmentally robust and an examination of long-term system operation will be presented.© (2010) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.