This book constitutes the refereed proceedings of the 12th International Conference on Conceptual Structures, ICCS 2004, held in Huntsville, AL, USA in July 2004.The 21 revised full papers presented together with 5 invited papers were carefully reviewed and selected for inclusion in the book. The papers are organized in topical sections on data and conceptual structures, concept lattices and concept graphs, conceptual frameworks for applications, and reasoning with conceptual structures.