Revision with unchanged content. In recent years, many jurisdictions around the world have moved from the vertically integrated power systems to the deregulated competitive electricity markets. Unlike the integrated systems, future prices are uncertain in the new competitive electricity markets. This price uncertainty generally introduces a great deal of complexity in optimal planning and operation of electric energy systems. This monograph deals with sort-term optimal operation planning in a competitive electricity market by forecasting future prices. Various forecasting techniques are applied to generate price forecasts, and the corresponding practical challenges are discussed. Optimization models are developed for the short-term operation of two typical demand-side electricity market customers, namely, a municipal water plant facility and an industrial load owning self-generation facilities. The generated forecasts are used as inputs to the optimization models and optimal schedules are derived. Economic impact of price forecast inaccuracies on the customers is also examined.