This book constitutes the refereed proceedings of the 5th International Conference on Spatial Information Theory, COSIT 3001, held in Morro Bay, CA, USA in September 2001. The 30 revised full papers presented together with three full keynote papers were carefully reviewed and selected from more than 70 submissions. The papers are organized in topical sections on geographical ontology and onthologies; qualitative spatio-temporal reasoning; formalizations of human spatial cognition; space, cognition, and information systems; human and machine approaches to navigation; language and space; and cognitive mapping.