This third course in the XR for Everybody specialization is geared toward the technical development of XR experiences. The course provides learners with a more technical mental model of XR technologies and the tools to approach XR development with confidence. It walks through the stages of development for both VR and AR projects, introducing the main XR development platforms as well as the key methods and tools. This third course also helps learners infer advanced XR requirements from physical/digital prototypes and teaches them how to differentiate major technical concerns, estimate development costs, and plan research necessary to advance XR. This course also has an honors track that guides learners in the implementation of 3D, VR, and AR scenes in WebXR using A-Frame and in Unity, and helps them generate a development plan with clear milestones and deliverables.