Abstract: This thesis examines the origins, selection process, training, promotion and general performance, at battalion and regimental level, of combat officers of the New Zealand Expeditionary Forces of the First and Second World Wars. These were easily the greatest armed conflicts in the country’s history. Through a prosopographical analysis of data obtained from personnel records and established databases, along with evidence from diaries, letters, biographies and interviews, comparisons are made not only between the experiences of those New Zealand officers who served in the Great War and those who served in the Second World War, but also with the officers of other British Empire forces. During both wars New Zealand soldiers were generally led by competent and capable combat officers at all levels of command, from leading a platoon or troop through to command of a whole battalion or regiment. What makes this so remarkable was that the majority of these officers were citizen-soldiers who had mostly volunteered or had been conscripted to serve overseas. With only limited training before embarking for war, most of them became efficient and effective combat leaders through experiencing battle. Not all reached the required standard and those who did not were replaced to ensure a high level of performance was maintained within the combat units. Casualties were heavy among the battalion officers, especially with platoon commanders. The constant need for replacements during both wars led to the promotion of experienced non-commissioned officers from the ranks who had proven their leadership abilities in the turmoil of fighting on the front line. Such measures further enhanced the performance of the New Zealand divisions, where a team ethos, reflective of the character of New Zealand society, was embraced. The opportunities for promotion on merit at all levels, regardless of previous civilian social class or occupation, provided a sense of egalitarianism seldom found in professional military forces. This, together with the familiarity between the officers and other ranks within the regional-based infantry battalions that formed the foundations of the forces, led to a preferred style of leadership that the New Zealanders responded well to. It was these officers who provided this leadership in the cauldron of battle who helped forge the expeditionary forces into elite fighting formations.