This book constitutes the refereed proceedings of the 4thInternational Conference on Security and Privacy in New Computing Environments, SPNCE 2021, held in December 2021. Due to COVID-19 pandemic the conference was held virtually. The 33 full papers were selected from 61 submissions and focus on security and privacy in new computing environments. The theme of SPNCE 2021 was “Secure Wireless Communication Systems: Infrastructure, Algorithms, and Management”.