This book constitutes the proceedings of the 9th International Workshop on Programming Multi-Agent Systems held in Taipei, Taiwan, in May 2011 in conjunction with AAMAS 2011, the 10th International Joint Conference on Autonomous Agents and Multiagent Systems. The 12 revised full papers presented together with 1 invited paper were carefully reviewed and selected for inclusion in the book. The papers are organized in topical sections on foundations of agent programming languages; multi-agent oriented programming; model checking; and papers of the participants of the multi-agent programming contest.

ProMAS-2011.- Part I: Foundations of Agent Programming.- Languages.- Logical Foundations for a Rational BDI Agent Programming Language.- (Extended Version).- Relating Goal and Commitment Semantics.- Part II: Multi-Agent Oriented Programming.- Developing a Knowledge Management Multi-Agent System Using JaCaMo.- Notes on Pragmatic Agent-Programming with Jason.- Integrating Expectation Monitoring into BDI Agents.- Part III: Model Checking.- Abstraction for Model Checking Modular Interpreted Systems over ATL.- MAS:Qualitative and Quantitative Reasoning.- State Space Reduction for Model Checking Agent Programs.- Part IV:Multi-Agent Programming Contest.- The Multi-agent Programming Contest 2011: A Resume.- HactarV2:An Agent Team Strategy Based on Implicit Coordination.- Implementing a Multi-Agent System in Python with an Auction-Based Agreement Approach.- Bogtrotters in Space.- A Gaia-Driven Approach for Competitive Multi-Agent Systems.