Increasingly, the armed forces of Western countries are outsourcing military tasks to private contractors. The aim is to enhance efficiency. However, an excessive outsourcing can have a negative effect on mission fulfilment. This raises the question of how far this practice can be allowed to go. Hitherto, the approach has been to assess the expedience of outsourcing in terms of capability categories in a one-time consideration of the balance between efficiency and effectiveness. However, the relationship between efficiency gains and loss of effectiveness depends to a considerable degree on the security situation. Decisions on outsourcing should therefore be made flexibly in accordance with the security environment.