Robert Langlands formulated his celebrated conjectures, initiating the Langlands Program, at the age of 31, profoundly changing the landscape of mathematics. Langlands, recipient of the Abel Prize, is famous for his insight in discovering links among seemingly dissimilar objects, leading to astounding results. This book is uniquely designed to serve a wide range of mathematicians and advanced students, showcasing Langlands’ unique creativity and guiding readers through the areas of Langlands’ work that are generally regarded as technical and difficult to penetrate. Part 1 features non-technical personal reflections, including Langlands’ own words describing how and why he was led to formulate his conjectures. Part 2 includes survey articles of Langlands’ early work that led to his conjectures, and centers on his principle of functoriality and foundational work on the Eisenstein series, and is accessible to mathematicians from other fields. Part 3 describes some of Langlands’ contributions to mathematical physics.