This paper traces the evolution of a component of a mechanical design from its initial inception to completion. This research focuses on the interplay of design objects, features, constraints, and design decisions. Based on empirical data extracted from verbal design protocols, a design terminology is developed. Constraints were identified in the protocol and classified according to their source, level of abstraction, and form or function orientation. A structure for constraints was also developed which decomposes the constraints and classifies them into ten basic feature relationships.