This book collects the scientific papers presented at the 2nd Congress of the Italian Association for Artificial Intelligence, held in Palermo in October 1991. It displays the state of the art of both Italian and European scientific research in AI. The book begins with an invited paper by W. Wahlster et al. The bulk of the book is then divided into five parts on: - Knowledge representation (18 papers), - Knowledge acquisition (5 papers), - Natural language (5 papers), - Perception and robotics (5 papers), - Architecture and technologies (5 papers). A section containing short papers completes the book. The high quality of the papers reflects massive research activity mainly devoted to the theoretical aspects of AI, but clearly aimed at consolidating the results already achieved. Several contributions are oriented to the technological aspects of AI.