This document discusses the challenges of changing requirements in engineering projects and proposes an approach called "third order requirements engineering" to address them. It argues that most current approaches (first and second order) only consider the solution and procurement process, not the evolving identity of the client. Third order requirements engineering explicitly considers how the client's identity evolves over time. The requirements process transforms a "naive" client's infinite demands into a "mature" client's realistic desires through iterative refinement of the specification. Understanding this evolution of client identity is key to adequately addressing changing requirements.