Web software applications have become complex, sophisticated programs that are based on novel computing technologies. Their most essential characteristic is that they represent a different kind of software deployment—most of the software is never delivered to customers’ computers, but remains on servers, allowing customers to run the software across the web. Although powerful, this deployment model brings new challenges to developers and testers. Checking static HTML links is no longer sufficient; web applications must be evaluated as complex software products. This paper focuses on three aspects of web applications that are unique to this type of deployment: (1) an extremely loose form of coupling that features distributed integration, (2) the ability that users have to directly change the potential flow of execution, and (3) the dynamic creation of HTML forms. Taken together, these aspects allow the potential control flow to vary with each execution, thus the possible control flows cannot be determined statically, prohibiting several standard analysis techniques that are fundamental to many software engineering activities. This paper presents a new way to model web applications, based on software couplings that are new to web applications, dynamic flow of control, distributed integration, and partial dynamic web application development. This model is based on the notion of atomic sections, which allow analysis tools to build the analog of a control flow graph for web applications. The atomic section model has numerous applications in web applications; this paper applies the model to the problem of testing web applications.