Abstract. The Fuel Cycle, which includes plasma fuelling and exhaust, as well as exhaust processing and isotope separation, is one of the key elements on which the successful operation of ITER will depend. This paper provides an overview of this system, reviewing requirements, operational scenarios, and the integration of the various subsystems using the ITER fuel cycle dynamic simulation program CFTSIM. The requirements to provide a plasma fuelling rate of 200 Pam3s- 1, with a flat-top burn of 400s and a repetition rate of two pulses per hour have the greatest influence on the design. However, while a flat-top burn of 400s is the initial design basis, the capability to extend the pulse to 3,000s in the longer term is essential from an operational perspective.