This book describes a methodological, model-driven approach to context-awareness and adaptivity in the field of Web Engineering and is based on the dissertation "Model-Driven Design of Context-Aware Web Applications" by the author. The described modeling approach is one of the first attempts to enlarge the applicability of adaptive application features in the Web from so-called "adaptive hypermedia systems" to "context-aware Web applications". While the former typically are based on a user model that is dynamically updated based on the observation of the user's navigation actions, the latter are based on a more complex context model and active, context-triggered application features. The research described in this book is applied in the context of WebML (the Web Modeling Language), yet its contribution is general in nature and can be ported to other modeling languages as well.