The network extension theory and its applications for analysis of circuits are introduced. Developed just in recent years

the theory deals chiefly with the properties of networks when some changes in their construction take place

providing a new approach for circuit analysis. The approach is efficient especially for the treatment of modifications and connections of networks and for the generation of symbolic network functions of large scale networks. Some practical techniques are discussed in detail. Several examples of the approach are given to show its efficiency and simplicity.