Intelligent agents are one of the most important developments in computer science in the 1990s. Agents are of interest in many important application areas, ranging from human-computer interaction to industrial process control. The ATAL workshop series aims to bring together researchers interested in the core aspects of agent technology. Speci?cally, ATAL addresses issues such as th- ries of agency, software architectures for intelligent agents, methodologies and programming languages for realizing agents, and software tools for developing and evaluating agent systems. One of the strengths of the ATAL workshop series is its emphasis on the synergies between theories, infrastructures, architectures, methodologies, formal methods, and languages. This year's workshop continued the ATAL trend of attracting a large n- ber of high-quality submissions. In more detail, 75 papers were submitted to the ATAL-99 workshop, from 19 countries. After stringent reviewing, 22 papers wereacceptedforpresentationattheworkshop.Aftertheworkshop,thesepapers were revised on the basis of comments received both from the original reviewers and from discussions at the workshop itself. This volume contains these revised papers.

Section I: Agent Theories.- Reasoning about Visibility, Perception, and Knowledge.- A Spectrum of Modes of Knowledge Sharing between Agents.- Observability-based Nested Belief Computation for Multiagent Systems and Its Formalization.- On the Correctness of PRS Agent Programs.- Incorporating Uncertainty in Agent Commitments.- Section II: Agent and System Architectures.- Rational Cognition in OSCAR.- Agents for Information Broadcasting.- On the Evaluation of Agent Architectures.- Toward a Methodology for AI Architecture Evaluation: Comparing Soar and CLIPS.- Reactive-System Approaches to Agent Architectures.- A Planning Component for RETSINA Agents.- A Scalable Agent Location Mechanism.- Section III: Agent Languages.- Reactivity in a Logic-Based Robot Programming Framework.- Extending ConGolog to Allow Partial Ordering.- Operational Semantics of Multi-Agent Organizations.- Open Multi-Agent Systems: Agent Communication and Integration.- Toward Team-Oriented Programming.- Section IV: Agent-Oriented Software Engineering.- Agent-Oriented Software Engineering.- Multiagent System Engineering: The Coordination Viewpoint.- Using Multi-context Systems to Engineer Executable Agents.- Structuring BDI Agents in Functional Clusters.- Towards a Distributed, Environment-Centered Agent Framework.- Section V: Decision Making in a Social Context.- Variable Sociability in Agent-Based Decision Making.- Cooperation and Group Utility.- Relating Quantified Motivations for Organizationally Situated Agents.- The Role and the Impact of Preferences on Multiagent Interaction.- Deliberative Normative Agents: Principles and Architecture.