Since the author published his book, "Power System Economics", in 1983, fundamental changes have taken place worldwide in electricity economics and planning. The methods developed in the 1960s and 1970s, outlined in that book, emphasized national economic development programmes and prescribed pricing from such programmes, optimizing over the long term. These methods were based upon long-term demand forecasts, elaborate probabilistic risk analysis for reliability, a discounted cash flow approach to project costs and benefits, and long-run marginal costs pricing. Almost everywhere, in developed and developing countries alike, this approach is giving way in planning emphasis to methods based on short-term, short payback development programmes, together with actual time-of-use, dynamic and "spot" pricing, possibly set in real time. Furthermore, much greater emphasis is given today in electricity supply to the following: consumer response; private capital; private utilities; demand management; energy efficiency; conservation, and environmental maintenance. This volume makes full use of the subject matter of the previous book, and takes into account the change of emphasis described above. It also introduces the issues and options likely to arise in power system economics and planning in the late 1990s and beyond.