Book excerpt: This book constitutes the thoroughly refereed post-proceedings of the Third International Workshop on Declarative Agent Languages and Technologies, DALT 2005, held in The Netherlands in July 2005 as an associated event of AAMAS 2005, the main international conference on autonomous agents and multi-agent systems. The 14 revised full papers presented were carefully selected during two rounds of reviewing and improvement for inclusion in the book. The papers are organized in topical sections.