Book excerpt: The advent of lasers has made possible a number of optical-based systems and applications such as the compact disc (CD), laser printers, fiber optic communications, laser surgical instruments, etc. Unfortunately, while lasers permit these diverse applications, safety concerns must be addressed. A solution being pursued is the development of optical limiter materials that transmit at low intensities while changing their optical characteristics, e.g. absorption or index of refraction, when exposed to the laser's higher irradiances. Topics covered in this book relate directly to the computational design and synthesis of new optical molecules. Research on the design of limiter devices is also featured. Materials addressed include liquid crystals, organic polymers, organic dyes, C60, colloidal arrays and suspensions, transition metal oxides, semiconductors and photorefractive oxides. Topics include: modelling and solid state optical limiters; thin film and solid state optical limiters; saturable and reverse-saturable absorbers; liquid optical limiters and liquid crystalline and other optical limiters.