Abstract : CAVE-like display systems (collectively known as Immersive Projection Technology, or IPT displays) are rapidly replacing head-mounted displays (HMD) as the display of choice in applications that benefit from a high level of immersion. We propose an in-depth study of interaction within IPT systems, and argue that basing interaction on techniques developed for other types of immersive systems is a flawed approach. We distinguish between three common situations of use of an IPT: single-user, groups of co-located users and geographically distributed users collaborating in a shared virtual environment. Through a series of design and experimental phases have demonstrated interaction techniques customised for these usage scenarios. The results of this project will be relevant for all developers, engineers and scientists who anticipate prototyping applications on next-generation immersive systems. We have made the systems we developed available for common use.