Adaptivity plays a central role for Web-based assistance to work and training processes. In the last decade, learning and work systems have evolved, from single-user sequential scenarios to multi-actors rich learn-flows and workflows. Within the Semantic Web, resources, activities, and actors are referenced semantically using ontologies, while the user model focuses more on the user’s cognitive state than on simple interface adaptation. The assistance model elaborated in this chapter is composed of a hierarchy of rule-based agents that interacts with semantic annotation of scenario components such as actors, activities, and resources. Ontology-based assistance in multi-actor scenarios is a contribution towards the adaptive semantic Web.