Three articles that featured in HEJ's April and November 2013, and April 2014 issues, focused, respectively, on the roles and responsibilities of those operating and managing medical gas pipeline systems, the MGPS Permit to Work System, and how to raise and complete the MGPS Permit to Work. In this fourth and final part of this 'series' of medical-gas system-related guidance articles by the same author, experienced medical gas systems trainer, Geoff Dillow, explains how to prepare, implement, monitor, and review, the MGPS Operational Policy.