John Muir (1838 – 1914) is widely known as the spokesperson of the American movement for the preservation of wilderness, mainly as a result of his leadership of the campaign opposing the creation of a dam in the Hetch Hetchy Valley in the Sierra. Born in Scotland, Muir was brought up in a strict household which adhered to the Reformed Protestant tradition. At the age of eleven years he moved to America where his family settled. Muir integrated Biblical language and imagery, Romanticism and science to develop his idiosyncratic theology of nature during his years in the Sierra, while studying the natural history and geology of that place. This thesis examines Muir’s books in order to answer the question: Is Muir a Scientist or a Theologian? It concludes that Muir’s personal understanding of God and Creation formed the basis of his writing, that his religious ideas infused his scientific thinking, and that these were evident in his arguments for preservation of wild places.