The present book is a natural outgrowth of Rescher's longstanding preoccupation with the rational systematization of our knowledge as manifested in such earlier works as Cognitive Systematization, and Complexity. Accordingly, the role of principles in human affairs is crucial and ubiquitous. Principology, the theory of principles—underdeveloped through it may be—is accordingly bound to find a significant place in the sphere of philosophical inquiry regarding matters of thought and action.