This book constitutes the refereed post-proceedings of the 4th International Conference on Networked Systems, NETYS 2016, held in Marrakech, Morocco, in May 2016. The 22 full papers and 11 short papers presented together with 19 poster abstracts were carefully reviewed and selected from 121 submissions.They report on best practices and novel algorithms, results and techniques on networked systems and cover topics such as multi-core architectures, concurrent and distributed algorithms, parallel/concurrent/distributed programming, distributed databases, cloud systems, networks, security, and formal verification.