The JET Active Gas Handling System (AGHS) consists of a number of interlinked processing systems for recovery of the radioactive tritium, its purification, separation from the other hydrogen isotopes, storage and recycling to the JET machine. To meet the stringent safety requirements and the multiplicity of monitoring, control and operational tasks, a plant-wide process control system was designed to integrate all tritium related functions. The AGH Control system is based on an industrial Distributed Control System (DCS) by Fischer & Porter which was tailored to the specific sequential/batch, closed loop and coordinating needs of the plant. Approximately 3600 Input Output (I/O) points are interfaced to the front-end consisting of 16 processors linked via a dual Ethernet Highway network and fast (0.1 s) 4-loop controllers. Three identical console processors support 6 screens which can access any point of the plant. The system has data-links to PLC's, analytical instrumentation and the JET CODAS network. It was installed in a dedicated control room in 1990 and is now being tested and commissioned. This paper describes the design of the system, the selection of the DCS hardware and the special emphasis which was put on the preparation of the software requirements and documentation.