Optical amplifiers are the fundamental building blocks required for the development of future all-optical networks. The elimination of electronic bottlenecks will allow the development of new network architectures which, for example, will enable the realisation of a network that has the flexibility to meet rapid changes in demand for capacity. In the past two years there has been dramatic progress in the development of both semiconductor and fibre amplifiers, to the extent that these components can now be considered for real applications.