A Smart Environment is an environment enriched with disappearing devices, acting together to form an “intelligent entity”. In such environments, the computing power pervades the space where the user lives, so it becomes particularly important to investigate the user’s perspective in interacting with her surrounding. Interaction, in fact, occurs when a human performs some kind of activity using any computing technology: in this case, the computing technology has an intelligence of its own and can potentially be everywhere. There is no well-defined interaction situation or context, and interaction can happen casually or accidentally. The objective of this dissertation is to improve the interaction between such complex and different entities: ...