This book is concerned with the optical technologies that enable implementation of the manifold wearable display devices that are emerging in today?s technology market, such as VR and AR headsets, smart glasses (such as Google Glass) and smart eyewear. It covers all optical sensors used in such wearable devices such as eye tracking and eye gaze sensors, eye gesture sensors, hand motion and gesture sensors and so on. Optical platforms include all tools found today in the optical engineer?s toolbox such as: refractives, reflectives, catadioptric, micro-optics, segmented Fresnel, diffractives, holographics and even meta materials and Parity time symmetric optics. Optical technologies include both smart phone type displays (OLED), and micro-displays (LCOS, LCD, iLED, OLED, MEME scanner, fibre scanner, dynamic diffractive microdisplays, etc). The book also reviews the various domains in which such devices are used today, starting with the military and defence sectors (historically the first ones), going to enterprise sectors and specialized markets (medicine, law enforcement, firefighting, engineers, sports and consumer markets).