Tracing requirements helps verify system features against the requirements specification, identify error sources, and — most importantly — manage change. We describe a tool called TOOR (Traceability of Object-Oriented Requirements), based on Joseph Goguen's broad view of requirements, which suggests that not only technical but also social factors play a significant role in software development. Of course, the requirements themselves are not necessarily object-oriented. Our tool's name is derived more from its use for object-oriented development and its object-oriented implementation, which allows the definition of classes and subclasses of objects and relationships among objects. Requirements traceability is our primary topic, but the scope of the tool reflects our view that requirements issues are pervasive and occur throughout the life cycle. Therefore, requirements traceability should be available at all times, and traceability of any desired artifacts should be supported.