This book is the outcome of 25 years of research on how to model and use context in real-world applications on a spectrum from technology-centered (SEPT, SART) to human-centered (e.g. FlexMIm) applications, that is, from well-defined domains to more fuzzy ones. It presents: · an operational definition of context that initiated a conceptual framework associated with an implementation framework, the Contextual-Graphs (CxG) formalism · the use of the research for designing a future type of AI systems, namely the context-based intelligent assistant systems There is a large international and interdisciplinary community of individuals convinced by the promises of bottom-up approaches as an alternative to the current top-down approaches in AI mainly. Practitioners will discover a tool easy to understand and use. Researchers will dispose of a comprehensive conceptual framework facilitating its extension on aspects not yet covered beyond group activity modeling, in the realm of the research on AI systems.