Polyethylene pipes for industrial and nunicipal vises have been installed since 1960, thirty years ago. Insert Renewal of gravity flow sewers is a widely accepted process using high density polyethylene pipe (ie: a pipe in a pipe). The placement of high density polyethylene (HUE) liner in a high pressure metal pipe began in the early 1960's. That 60's technology was advanced during -the 1980's using an expanded liner approach based on the ductility, toughness, and durability of HDPE, as well as using more effective installation equipment, product design, and construction methods. Ihe 1980's innovations were directed towards longer distance, higher pressure, transport pipelines in sizes of 2" (51mm.) through 24" (610mm.) diameter. During the last decade, a new proliferation of HDPE lining products and processes have evolved to meet the challenges of the 1990's. This paper briefly evaluates the requirements and effect of each design and installation approach on the HDPE liner. The growing industry of HDPE lining of pipes has expanded to oil patch downhole tubulars, transport pipelines (oil, gas, and product), industrial/municipal water and gas distribution mains, and in some cases, nunicdpal sewers. The four generic processes considered herein are: 1. liner Expansion 2. liner Rolldown Reduction 3. liner Hat Swage Reduction 4. liner Visco-elastic Reducticn