J.R.R. Tolkien was strongly conscious of the importance of order, and order is a prominent force in his works. However, while in the past twenty-five years his writings, especially those fictional works dealing with his "secondary world" of "Arda", have been the subject of much critical commentary, the importance of order has not been comprehensively discussed. This thesis investigates the nature and function of order in Tolkien's major fictional works, The Silmarillion, The Hobbit and The Lord of the Rings, with references to his critical writings and minor fictional works where relevant. The introduction notes the importance of order to Tolkien as an individual in the "primary world" (this world), demonstrating some of the ways in which order and chaos were felt by Tolkien to operate in his own life. The second chapter, which begins the discussion of "Arda", shows that order originates with the Creator of the World. The development of chaos during the making of Arda and the nature of the world which results from the order-disorder struggle are examined. The five following chapters demonstrate the all-encompassing role of the order-chaos conflict which pervades and influences structures formed by the societies of Ards and the actions of their members. Chapter III investigates the connection between order and the concept of "heroism" as evident in the behaviour of individuals. The role of order in the relationships among the members of different social groups and among characters and the world around them is examined in the fourth, fifth and sixth chapters. The seventh chapter looks at the links between order and past history in Arda and traces the development of events under the influence of the two forces. The last chapter concludes that Tolkien's characters, in their relationships with others and with their world, are agents of order in a way which differentiates them from traditional heroes of myth and fairy-story, a difference which is also evident in the stories of many fantasy writers working in the past quarter-century. The depiction of order in Tolkien's secondary world, especially as represented by the attitudes and actions of its inhabitants, is seen as a central and yet all-pervasive factor in his fictional writings.