Arriving at an appropriate design for the renewal of an existing buried pipe structure requires a markedly different approach than the design of a new buried pipe installation and is generally more difficult. The design engineer for a new pipe project can further overcome the challenges of the installation site by choosing between a rigid pipe material and a flexible pipe material to address the project site's specific installation and/or safety issues. In a pipe renewal design, the design engineer works with a pipe in given condition, as well as with the given choice of liner material and method of installation. This introduction presents an overview of the key concepts discussed in the subsequent chapters of this book. The book provides guidance to the consulting engineers tasked with designing flexible close-fit liners for the renewal of existing gravity pipe applications in a form that is readily usable.