Over the past three decades, as computer and display technology advanced along the path laid out by Moore’s Law of miniaturization and functionality, many writers presented scenarios for augmented reality (AR) displays centered on bringing information to the individual. Initially, the emphasis was on the individual experience, so the technology, which did not pursue a see-through geometry, seemed viable. When the initial solutions—a generation of look-at displays resting on the nose bridge—appeared around 2000, the market did not embrace it. Suddenly now, social media has burst on the scene, and wireless access has become ubiquitous. The result is a renewed research interest in a family of see-through head-worn displays (HWDs) enabling real-time interaction throughout the global community. See-through HWD design inherently requires an interdisciplinary approach; optical engineering, opto-mechanics, ergonomics, and psychology are all keys to the design process. The last decade has seen a game-changing technology emerge, the organic light-emitting display (OLED), replacing what was thought to be a game-changer, the light-emitting diode (LED) illuminator combined with a liquid crystal display (LCD) or liquid crystal on silicon (LCoS) display, which in turn had replaced the initial technology, the mini-CRT. The first 4 k-format (4096 × 4096) OLED displays have been demonstrated, and 2048 × 2048 OLED displays have been available for over a year and have opened new doors for HWD applications. The current industry goal is to supply a system that will receive widespread consumer acceptance (meaning millions of units need to be manufactured in months once a design-for-manufacture point is selected). The system must be low-cost (hundreds of dollars to the consumer) and approach an eyeglass format with a resolution that approaches the human visual system extending into the peripheral FOV. This chapter first motivates the potential benefits of HWDs, especially in see-through mode, and examines key technology pathways that build on historical highlights. Market barriers to the emergence of eyewear format HWDs are then highlighted. Optical architectures for see-through HWDs along with key factors and functions required of a successful see-through HWD are then reviewed. Specifically, building on optical design fundamentals, the key engineering concepts and constraints are presented, and solutions discussed. Particular emphasis is placed on differentiating the concept of an eye pupil and an operational eyebox. Next, the Lagrange invariant (LI), which sets fundamental limits in the optical design of HWDs, is examined. Following the presentation of see-through HWDs, two differentiated solutions are presented: the head-mounted (worn) projection display (HMPD) and the retinal scanning display (RSD), along with a brief overview of waveguided HWDs. The chapter concludes with a brief discussion of some of the current research that may affect the solution that the market selects, including freeform optical surfaces.