The three volume set LNAI 5177, LNAI 5178, and LNAI 5179, constitutes the refereed proceedings of the 12th International Conference on Knowledge-Based Intelligent Information and Engineering Systems, KES 2008, held in Zagreb, Croatia, in September 2008. The 316 revised papers presented were carefully reviewed and selected. The papers present a wealth of original research results from the field of intelligent information processing in the broadest sense; topics covered in the third volume are intelligent data processing in process systems and plants; neural information processing for data mining; soft computing approach to management engineering; advanced groupware; agent and multi-agent systems: technologies and applications; engineered applications of semantic Web; evolvable hardware and adaptive systems; evolvable hardware applications in the area of electronic circuits design; hyperspectral imagery for remote sensing; immunity-based systems; innovations in intelligent multimedia systems and virtual reality; intelligent environment support for collaborative learning; intelligent systems in medicine and healthcare; knowledge interaction for creative learning; novel foundation and applications of intelligent systems; skill acquisition and ubiquitous human computer interaction; smart sustainability; unsupervised clustering for exploratory data anlysis; and use of AI techniques to build enterprise systems.