In this chapter we describe the product line models, and show how to apply them for developing and evolving Web products. A product line captures the common and variable aspects of software systems as key assets under a common architecture. Software companies are increasingly adopting this approach in order to accelerate the development of families of similar software products. In certain domains, such as the Web systems, development and maintenance operations are required more often. New techniques to engineer Web sites are needed in order to reduce the time to market for the Web products and to maintain the systems afterward. The authors believe that understanding the notion of lightweight product line and the role that the architecture plays will help software engineers in the construction of software products, and they will be able to manage the evolution effectively against future changes.