This volume contains the papers presented at the 21st Annual IFIP WG 11.3 Conference on Data and Applications Security (DBSEC) held July 8–11 in - dondo Beach, California, USA. The purpose of the DBSEC conference is to disseminate original research results and experience reports in data and app- cations security. In response to the call for papers, 44 submissions were received. Following a rigorousreviewingprocess,18high-qualitypaperswereacceptedforpresentation and publication. In addition, two short papers were selected for poster pres- tation. The conference program also included one invited talk and one panel discussion. We believe that the program includes a balanced mix of practical experiences and theoretical results that consolidate existing work and suggest emerging areas of interest for researchers in data and applications security. The continued success of the DBSEC conference is due to the e?orts of many individuals. We would like to thank all of the researchers that submitted - pers to DBSEC for consideration, and the Program Committee members and additional reviewers for making the review process fair and thorough, and for providing valuable suggestions on each submission. We are also indebted to the invited speakers and panelists for their contributions to the success of the c- ference.