This article describes the variety of optics required for XR (extended reality) devices. For AR glasses, this includes waveguides and other technologies such as birdbath combiners, whilst for VR headsets, solutions include pancake, Fresnel, and aspheric lenses. Across XR devices, different optics solutions are required based on the intended use case, with a variety of factors contributing to the suitability of an optics technology for a specific device. Factors include weight, optical efficiency, image quality, form factor, and cost.