The loop plant is a fruitful area for operations modeling.Because it can have many configurations and detailed structures, and because over 30 percent of the total telephone work force interacts with it, it is physically and operationally complex, and modeling is often the only way to arrive at an understanding of the basic principles underlying its operation. This article provides an introduction to the loop plant modeling papers which follow and includes both a description of the loop plant and brief descriptions of the individual papers.