This book constitutes the refereed proceedings of the 4th International Conference on Industrial Applications of Holonic and Multi-Agent Systems, HoloMAS 2009, held in Linz, Austria, August 31 - September 2, 2009. The 31 revised full papers presented were carefully reviewed and selected from 47 submissions. The papers are organized in topical sections on introduction and motivation, knowledge-centered approaches, selected theoretical aspects, MAS scheduling and simulation, holonic systems for manufacturing, and MAS and Holonic applications.