Traceability is about documenting the relationships between layers of information, for instance, between system requirements and software design. Many software development tools manage design relationships, for instance, between modeling elements (such as classes) and source code, or between tasks and source code files. Whatever development scale we engage in, we systematically apply information traceability. It's a vehicle for thinking about the way the software meets its requirements; it captures design rationale to help others understand and review; and it gives us far greater confidence in managing future changes.