This study is based upon a comprehensive survey of Leslie Mitchell's written work. This includes letters, manuscripts, rare material and stories and articles which have not teen cited before, as well as the fiction and non-fiction which was published under either his own name or the pseudonym of Lewis Grassic Gibbon. In Part One, I examine the main ideas at play in this body of work and conclude that there are two primary ones: these are considered under the terms which Mitchell used to compliment Quetzalcoatl, a legendary figure from ancient American history. These two ideological impulses are personal to Mitchell, and yet both are in sympathy with modern intellectual developments. His political ideas are considered under the term "reformer", which concisely reflects his radical sympathies, his interest in anarchism and communism, and in political movements of a universal scope. The germ of Mitchell's philosophy lies in the word "blasphemer". Firmly opposed to the theist stance, he wavered between an angst-ridden scepticism and a romantic form of pantheism; but in his most mature work, he finds a happy medium between these poles, ultimately providing a vision of a religious character which is based upon empirical principles. In a separate subchapter, I investigate Mitchell's relationship with diffusionist theory as a secondary influence. In Part Two, I turn my attention to the fiction, paying particular attention to the beliefs of the "reformer" and the "blasphemer" as they are manifested in his stories and novels. The study of the shorter fiction is the most comprehensive to date, dealing with rare stories and work which has not been considered previously. Yet although Mitchell's personal philosophy can be seen developing in the English stories, it is more fully implicated in the Scottish ones, of which 'Clay' and 'Forsaken' are the finest, the former as the creation of the mature "blasphemer", and the letter as the work of the mature "reformer". The major fiction is equally variable. The early novels are artistically immature but intellectually stimulating, and the invigorating; realism and profundity of the Empirical fiction makes the Imaginative Romances appear anaemic in comparison. Spartacus is undoubtedly the finest Mitchell novel, and in it the "reformer" capitalizes upon the achievement of the "blasphemer", presentingradica-1 political involvement as the only positive-exercise in an otherwise meaningless life. However, A Scots Quair is Mitchell's masterpiece, a unique experimental novel in which the author's political and philosophical ideas come to full fruition. Dealing positively with the major themes of life, with the search for political solutions and for spiritual fulfilment, its appeal is timeless.