Because the lasers coming off the production lines are much more stable, efficient, and controlled than in the past, today's engineers often do not have the insight into the technology as was required of first-generation laser engineers. However, important insights into the use and performance of the laser and optical systems can be lost unless we remind ourselves of the problems our predecessors had to face. There is a maximum power and energy that you can put into or transmit through your optical system; in many cases, this maximum is well below the laser-induced damage threshold. This tutorial explains the factors and constraints that limit the capability of optical materials, components, and systems. Measurement techniques, specifications, and an overview of the international standards are covered as well, in a concise, easy-to-read format.