This dissertation has focused on better understanding the shifting web paradigm and the consequences of moving from the classical multi-page model to an Ajax-based single-page style. Specifically to that end, this work has examined this new class of software from three main software engineering perspectives. Software Architecture: to gain an abstract understanding of the key architectural properties of Ajax applications; Software Reengineering: to understand the implications of a migration from classical multi-page web systems to single-page Ajax variants. Software Analysis and Testing: to explore strategies for analyzing and testing this new breed of web application. The work presented in this dissertation aims at advancing the state-of-the-art in comprehending, analyzing, and testing standards-based single-page web applications, by means of a new architectural style, a significant set of techniques and tools, and case study reports. These contributions are aimed at helping software and web engineers better comprehend and deal with the complexity of highly dynamic and interactive web systems.