Galen's treatises on the classification and causation of diseases and symptoms are an important component of his prodigious oeuvre, forming a bridge between his theoretical works and his practical, clinical writings. As such, they remained an integral component of the medical teaching curriculum well into the second millennium. In these four treatises (only one of which has been previously translated into English), Galen not only provides a framework for the exhaustive classification of diseases and their symptoms as a prelude to his analysis of their causation, but he also attempts to establish precise definitions of all the key terms involved. Unlike other of his works, these treatises are notably moderate in tone, taking into account different views on structure and causation in a relatively even-handed way. Nonetheless, they are a clear statement of the Dogmatic position on the theoretical foundations of medicine in his time.