Development of thermal management strategies in the design of subsea oil and gas production systems is critical for prevention of solids deposition such as hydrates and wax formation during turndown and shutdown scenarios. Passive insulation provides no control of fluid temperature and forces the operator to depressurise the pipeline following a shutdown and ‘no touch’ period i.e. time after which the fluid falls below the hydrate temperature. For deep water and ultra-deep water applications this approach would be ineffective as the large riser static head would prevent the pipeline pressure being reduced below the hydrate formation pressure. In these cases there is a requirement for active heating or dead oil flushing. Active heating provides the capability to monitor and control the fluid temperature during start up, shutdown and turndown operations. Several electric and hot fluid circulation active heating systems are in operation as part of bundle or pipe in pipe systems. This paper will review current active heating system designs in pipe-in-pipe (PiP) and bundle systems. In light of recent projects that have employed hot fluid circulation systems, the flow assurance challenges and subsequent design to ensure complete system functionality across the life of field will also be discussed.