The authors propose original basic principles of electric network development optimization under the conditions of liberalized electric power markets. The following aspects are analyzed: 1) the structure, elements and functions of a liberalized electric power market; 2) the optimization of electric networks as an element of their sustainable development and management. The paper considers in detail the methods for: 1) assessment of supply reliability, 2) taking into account the information uncertainty, 3) complex optimization of networks and power stations, 4) application of information technologies in planning of sustainable development.