This chapter provides a comprehensive introduction to XR, an umbrella term encompassing VR, AR, and MR. These immersive technologies enable increasingly seamless interactions between users and digital content, effectively blending the physical and VWs. The chapter traces the historical development of XR, from early prototypes like the Sensorama and the first HMDs to the emergence of AR in the late twentieth century. It highlights the technological advancements—such as improvements in computing power, graphics, and sensors—that have fueled XR’s evolution into accessible, sophisticated systems. In parallel, research in HCI continues to drive innovation in this space. Concluding with a focus on the fashion retail sector, the chapter introduces how XR is being integrated into industry practices to create immersive, interactive, and personalized shopping experiences. By framing XR within both historical and applied contexts, this section lays the groundwork for understanding its transformative potential in fashion and beyond.