"Wilson's book is ground-breaking and thought-provoking, and indispensable for every serious student of hugely influential core aspects of Augustine's thought." -- Professor Karla Pollman, University of Bristol on Dr. Ken Wilson's "Augustine's Conversion". This book summarizes Dr. Wilson's "ground-breaking" doctoral thesis at the University of Oxford which was published by Mohr Siebeck in 2018 as "Augustine's Conversion from Traditional Free Choice to 'Non-free Free Will': A Comprehensive Methodology". With a new audience in mind, Dr. Wilson presents his extensive research on free will in ancient and early Christian thought in a shorter and more accessible format with translations of the ancient and modern foreign languages in plain English. Dr. Wilson first provides readers with essential background information on free will in the ancient philosophies and religions of Stoicism, Gnosticism, Neoplatonism, and Manichaeism. He then guides his readers through the writings of the earliest Christian authors who wrote on free will. Finally, Dr. Wilson explores a curious split between St. Augustine's early and later writings and shows how the ideas presented in Augustine's later writings became the foundation for modern Calvinist (Reformed) theology, also known as Augustinian-Calvinism.