This thesis examines the development of Australian Army jungle warfare doctrine and training during the Second World War. The Australian Army transformed itself from a military force ill-prepared for conflict of any type in 1939 into one of the most professional, experienced and highly trained forces in jungle warfare in the world by 1945. The thesis analyses how this transformation occurred and, in doing so, provides a case study in institutional learning. Attempting to discover how an organisation learns is vital: unless these processes of adaptation are identified, it is extremely difficult for an organisation to apply successfully the lessons in the future. For no institution is this more pertinent than for the military. Armed forces unable to adapt to unforeseen challenges were frequently defeated with often profound consequences. The thesis identifies this process of development and adaptation by the Australian Army from 1941 to 1945.