This chapter introduces the field of Mixed Reality that merges the real and virtual worlds seamlessly. To develop a Mixed Reality system, two fundamental problems should be addressed: tracking and user interface. Tracking in Mixed Reality is defined as the task of estimating the user's viewing pose. The goal of tracking is to achieve an accurate registration between real and virtual objects. In order to allow the user to interact e±ciently with the Mixed Reality scene, interaction techniques should be designed. A wide range of Mixed Reality applications, such as medical and entertainment applications, have been identified. We will focus on the new trends and applications in the area of Mixed Reality.