The Ajax developer's guide serves as an introduction to the new technologies, common issues, and debugging approaches to consider when developing with Web 2.0 technologies. Topics covered are why proxies become important in Web 2.0 applications, how Web 2.0 techniques can be used to enhance common Web development patterns, such as the Model-View-Controller (MVC) pattern, how to do dynamic communication using cometd style message publication and subscription, and how to debug Web 2.0-based applications.