What is XR? It s shorthand for a related set of new technologies that are changing the way we interact with the world and with each other: Virtual Reality, Augmented Reality, and Mixed Reality. To understand XR, you need to understand the technologies that enable it. If you understand the available technologies, how they are used, and what their future holds, you ll be well equipped to deal with XR as it rapidly evolves and converges. In this course, we will present an introduction to XR using a broadly chronological approach, focusing on how all of the underlying technologies came together at key moments in the history of XR to launch the concepts of Virtual Reality and Augmented Reality into the mainstream consciousness. Throughout the course, we ll give a brief description of each of the supporting technologies, some history about when it first came into use, limitations and future potential for improvement, and how it s used for AR, VR, and MR. As you learn about the technology, you ll also develop hands on experience in the field along two tracks. First, you will use Unity to build and run two simple XR applications on your own smartphone: a VR Museum app and a handheld Augmented Reality app. Second, you will brainstorm, define, visualize, and iterate your own original concept for an XR application, ending the course with a thorough and peer-reviewed XR Product Brief that you could use as the basis for future development. This is the first of three planned courses in Unity's XR Specialization, which include the Mobile VR App Development with Unity course as well as a future course focused on developing Augmented Reality (AR) applications with Unity.