This chapter describes Holmes's two great scholarly works: the twelfth edition of Kent’s Commentaries and The Common Law. Both books entailed a prodigious amount of legal research into the history of the common law. Both were written at a time when the law was rapidly changing to accommodate the increased commercialization and industrialization in the last half of the nineteenth century. Many men – most notably Christopher Columbus Langdell – were proposing new theories of common law decision-making, but Holmes was unique in his historical approach. This chapter explains Holmes’s approach and addresses some of the misunderstandings and criticisms it has generated.