Lars Levi Laestadius (1800-1861) is commonly known as the most influential North Swedish Lutheran revivalist in North Calotte during the 1800s and a founding character of the pietistic revival movement of Laestadianism. Academically, Laestadius was known for his expertise in botany, theology, and the mythography of the Sámi people. The influence of Laestadius’ religious and scientific work on the spiritual, intellectual and cultural life of North Scandinavia has been broad and lasting. This doctoral dissertation on philosophy and psychology of Laestadius focuses on his written theoretical work on anthropology and religion. It is the first attempt ever to examine the characteristics of Laestadius’ theology, psychology, and philosophy of religion as a whole from the philosophical perspective. It provides a historical contextualization and detailed analysis of the focal points of Laestadius’ theoretical thought as presented in his magnum opus, The Lunatic – An Insight Into the Order of Grace. This study also offers a versatile and informative presentation of Laestadius’ theoretical thought, including interpretations of Laestadius’ apology of Lutheran-pietism, psychological insights, philosophy of religion, and his critique and vitalist deconstruction of the central notions of Western metaphysical rationalism. The study also has relevance to the disciplines of Intellectual history, Cultural research and Sámi studies.