Well written requirements are the foundation of all well-engineered systems and successful engineering efforts. They define what must be achieved, how performance is measured, and under what constraints the system must operate. In critical software systems, requirements enforce discipline, accountability, and assurance. A poorly written requirement can cascade through the development lifecycle, generating integration errors, safety hazards, and mission failure. Requirements define the problem domain and, in doing so, directly increase engineering understanding of the system to be built.