Abstract. Nowadays, designers of Virtual Reality (VR) applications are faced with the choice of a large number of different input and output devices leading to a growing number of interaction techniques. Usually VR interaction techniques are described informally, based on the actions users can perform within the VR environment. At implementation time, such informal descriptions (made at design time) yield to ambiguous interpretations by the developers. In addition, informal descriptions make it difficult to foresee the impact throughout the application of a modification of the interaction techniques. This paper discusses the advantages of using a formal description technique (called ICO) to model interaction techniques and dialogues for VR applications. This notation is presented via a case study featuring an immersive VR application. The case study is then used to show, through analysis of models, how the formal notation can help to ensure the usability, reliability and efficiency of virtual reality systems. 1