The growing complexity of agent systems calls for models and technologies that allow for system predictability and enable feature discovery and verification. Formal methods and declarative technologies have recently attracted a growing interest as a means for dealing with such issues. This book presents revised and extended versions of 11 papers selected for presentation at the First International Workshop on Declarative Agent Languages and Technologies, DALT 2003, held in Melbourne, Australia in July 2003 during AAMAS; also included are 3 invited papers by leading researchers in the area to ensure competent coverage of all relevant topics. The papers are organized in topical sections on - software engineering and MAS prototyping - agent reasoning, BDI logics, and extensions - social aspects of multi-agent systems