Passengers and employees expect and deserve effective aviation security. This belief unites States and industry as they work in collaboration to prevent, detect, and deter the next attack. Because security resources are finite, professional security practitioners must focus on protecting the industry from the probable rather than what is possible. Risk management provides the framework for identifying and quantifying vulnerabilities. This “common sense” approach to security provides for a proportionate response and effective countermeasure development. The alternative is to squander security resources on defending industry assets against the most impossible and unlikely threats that may exist only in our imagination.