This book is the fifth in the successful line of Intelligent Agents volumes published in LNAI. It is based on the fifth workshop on Agent Theories, Architectures, and Languages (ATAL'98) held during the Agents World conference in Paris in July 1998. The 25 revised full papers included were selected from a total of 90 submissions during two rounds of reviewing. Also included are an introduction by the volume editors, two summaries of panel discussions held at the workshop, a classification of all papers published so far in the five Intelligent Agents books, and a subject index. This state-of-the art survey is essential reading for anyone interested in agent technology.