Engagement has become a fundamental research topic in Human-Computer Interaction (HCI). Extending the notion of traditional usability, HCI has focused on the hedonic properties of interactive systems. In particular, gameful design and multimodal interaction received much attention in the literature. However, despite a significant and growing body of research on engaging design, many interactive systems for learning, training and, health intervention suffer from low participation and massive

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... ition. The present work tackles this gap and investigates how interaction design can support a sustainable engagement with interactive systems. As engagement is a manifold construct that involves affective, cognitive and behavioral components. In this thesis, it is conceptualized from the perspectives of experience intensity and in terms of user behavior. These two perspectives are addressed in three threads of research: (i) game design for user engagement: effects of game elements on engagement, (ii) haptic interaction in engaging environments: effects of interaction modality on engagement, and (iii) assessment methods of user engagement in immersive environments: effects of embedded assessment methods on engagement. The thread on game design is twofold. This work presents the snacking framework, which consists of five game mechanics that facilitate a regular but brief play pattern. The snacking framework was first developed and evaluated using a casual game and then transferred onto a serious game. Adjacent to the snacking game mechanics, for a special case of serious games in the context of exposure therapy in Virtual Reality (VR), this work discusses an alternative approach to game design which employs an approach of playful user-generated content. The interaction design investigates the effects of haptic interaction on user engagement. This thread of research examines how static passive props both in VR as well as in the physical reality and interaction with sand – as a form of passive shape-changing props – in VR aff [...]