Over the past four decades, source criticism--the analysis of a writer's source material--has emerged as one of the most popular approaches in exploring the work of J.R.R. Tolkien. Since Tolkien drew from a wide range of disparate sources in the construction of his legendarium--from The Book of Lost Tales to The Hobbit to The Lord of the Rings, and beyond--an understanding of the sources Tolkien used, as well as how and why he incorporated them, can enhance readers' appreciation of his works immeasurably. This compendium by leading Tolkien scholars describes the theory and methodology for proper source criticism of Tolkien's works and then provides practical demonstrations of the approach. Ranging widely across Tolkien's works, as well as across the periods and genres from which he took inspiration, the essays provide the most balanced and comprehensive demonstration of source criticism ever collected in a single volume.