This volume contains papers presented at the fourth working conference on Communications and Multimedia Security (CMS'99), held in Leuven, Belgium from September 20-21, 1999. The Conference, arrangedjointly by Technical Committees 11 and 6 of the International Federation of Information Processing (IFIP), was organized by the Department of Electrical Engineering of the Katholieke Universiteit Leuven. The name "Communications and Multimedia Security"...