This book is the sixth in the successful line of Intelligent Agents volumes published in LNAI. It is based on the sixth workshop on Agent Technologies, Architectures, and Languages, ATAL'99, held in Orlando, Florida, USA in July 1999. The 27 revised full papers included were selected from a total of 75 submissions during two rounds of reviewing. Also included are an introduction by the volume editors and a subject index. The book is divided into topical sections on agent theories, agent and system architectures, agent languages, agent oriented software engineering, and decision making in a social context. This state-of-the-art survey is essential reading for anyone interested in agent technology.