Requirements for Plasma and First Wall Measurements on ITER

In this paper we outline the process that is in use for developing the requirements for plasma and first wall measurements on ITER. These requirements are the starting point in the selection, design and integration of the individual measurement systems that together make up the ITER diagnostic system. We describe the issues that have arisen in the defining process and we give the current status. We take a brief forward look at some aspects of the measurement requirements for a next step (DEMO).