The factors influencing the safe management of contractors on major hazard installations are discussed. Contractors are found to complete work without complying with corporate systems for a number of reasons which includes critical standards and systems not being agreed upon before the contract was signed, and the failure to understand critical corporate standards. The need for careful selection of contractors and checking that they have the experience in high hazard industries is necessary for successful management of contractors. Companies using contractors for maintenance activities also need to think carefully about defining the responsibilities for supervision and inspection activities.