This chapter presents Web Augmentation (WA) technologies as tools and techniques for end-user development. WA technologies differ from other web development technologies as they target at improving existing Web pages and not at creating new Web sites. These improvements can deeply alter the way users use and interact with Web sites. This chapter revisits the concept of WA and provides an overview of the main features that characterize WA technologies. This characterization is used to position and compare the various contributions that have been made in WA. To make things more concrete we provide an illustration of WA technology through a case study using a dedicated tool called WebMakeup. Despite all their advantages, WA technologies present some limitations that might result in challenges on the user side. These aspects are also presented and discussed , highlighting directions for future work in that domain.