This chapter covers ways of mounting individual axisymmetric lenses ~10 to ~250 mm (~0.4 to ~10 in.) in diameter. Mounting techniques for multiple-lens assemblies are discussed in Chapter 6. The preferred design is one in which the effects of manufacturing and assembly tolerances are minimal and the location and orientation of each optic are maximally benign to adverse environments. These conditions are hard to achieve in many designs—increasingly so as performance demands increase. First discussed is what is meant by “centered” optics and how centration is achieved. Next are methods of estimating the weight of typical lens elements and locating their centers of gravity. Techniques for preloading individual refracting elements axially are then addressed. Some designs provide direct metal-to-glass interfaces at or near the rim of the polished surfaces of the lens, while others encapsulate the lens rim locally or continuously with resilient elastomeric material. Different mechanical contours for the interfaces with the lens surfaces are considered along with the localized contact stresses in the glass and metal parts resulting from preloads. Some typical means of aligning individual lenses in their mount are also summarized.