The Canons and other later writings of the school of Mo-tzu, dating from about 300 B.C., contain nearly all that survives of the logic of ancient China, and its optics and mechanics, the only organized set of geometrical definitions, and the only fully rationalized system of ethics. They represent the high point of abstract rationality in traditional Chinese civilization, and are crucial documents for any inquiry into its achievements and limitations in logic and science. Unfortunately their formidable textual difficulties have hitherto made it impossible to use them with any confidence, and English translations of Mo-tzu, have omitted them. Western sinologists have generally ignored this rich material with the result that they have been forced to draw their conclusions about Chinese logic from the almost negligible remains of the Sophists. The present work begins with a general account of the school of Mo-tzu, its social basis as a movement of craftsmen, its isolated place in the Chinese tradition, and the nature of its later contributions to logic, ethics and science. The relation of Mohist thinking to the structure of the Chinese language is also discussed. The textual problems of the later writings, the grammar and style, the technical terminology, the significance of stock examples, and the overall organization of the documents, are then explored in detail. With the investigation of these preliminary questions, the possibilities of interpretation are confined within controllable limits. The edited and annotated Chinese text follows, with an English translation and commentary, a glossary, and a photographic reproduction of the unemended text from the Taoist Patrology.