Mixed Reality seeks to smoothly link the physical and data processing (digital) environments. In recent years, mixed reality has been the subject of growing interest. Although mixed reality systems are becoming more prevalent, we still do not have a clear understanding of this interaction paradigm. This article introduces a new interaction model called Mixed Interaction model. It adopts a unifying point of view on mixed reality by considering the interaction modalities that are involved for defining mixed environments. This article presents the model after explaining its foundations, applies it to describe and compare existing systems and shows its generative power for designing new forms of mixed interaction.