This book constitutes the proceedings of the 7th International Conference on Network and System Security, NSS 2013, held in Madrid, Spain, in June 2013. The 41 full papers presented were carefully reviewed and selected from 176 submissions. The volume also includes 7 short papers and 13 industrial track papers. The paper are organized in topical sections on network security (including: modeling and evaluation; security prools and practice; network attacks and defense) and system security (including: malware and intrusions; applications security; security algorithms and systems; cryptographic algorithms; privacy; key agreement and distribution).