The 12 revised full papers presented together with 1 invited talk and 3 invited papers - fully revised to incorporate reviewers' comments and discussions at the workshop - were carefully selected for inclusion in the book. The papers combine declarative and formal approaches with engineering and technology aspects of agents and multiagent systems, thus gaining more and more attention in important application areas such as the semantic Web, Web services, security, and electronic contracting.

The workshop on Declarative Agent Languages and Technologies (DALT), in its fourth edition this year, is a well-established forum for researchers interested in sharing their experiences in combining declarative and formal approaches with engineering and technology aspects of agents and multiagent systems. Building complex agent systems calls for models and technologies that ensure predictability, allow for the verification of properties, and guarantee flexibility. Developing technologies that can satisfy these requirements still poses an important and difficult challenge. Here, declarative approaches have the potential of offering solutions that satisfy the needs for both specifying and developing multiagent systems. Moreover, they are gaining more and more attention in important application areas such as the Semantic Web, Web services, security, and electronic contracting.