This book presents the proceedings of the 4th International Conference on Wireless Intelligent and Distributed Environment for Communication (WIDECOM 2021), which took place at University of KwaZulu-Natal, South Africa, October 13-15, 2021. The book addresses issues related to new dependability paradigms, design, and performance of dependable network computing and mobile systems, as well as issues related to the security of these systems. The main tracks include infrastructure, architecture, algorithms, and protocols. The goal of the conference is to provide a forum for researchers, students, scientists and engineers working in academia and industry to share their experiences, new ideas and research results in the above-mentioned areas.