The nature of the military ordinariate is a comprehensive examination of the ecclesiological role of military ordinariates within the Catholic Church. The author, Torbjørn Olsen, analyzes the relationship between the particular churches and the military ordinariates, which represent a special form of church structure. This study begins with a historical overview of the Thirty Years' War and highlights the development up to the Second Vatican Council and the apostolic constitution 'Spirituali Militum Curae'. The work addresses the challenges and questions arising from the affiliation of soldiers and their families with military ordinariates and explores to what extent these can be considered particular churches in a theological sense. Through a critical analysis of current developments, particularly in South America, the book offers valuable insights into the complex relationship between the military and the church.