This book constitutes the refereed proceedings of the 12th International Conference on Security, Privacy, and Anonymity in Computation, Communication, and Storage, SpaCCS 2019, held in Atlanta, GA, USA in July 2019. The 37 full papers were carefully reviewed and selected from 109 submissions.The papers cover many dimensions including security algorithms and architectures, privacy-aware policies, regulations and techniques, anonymous computation and communication, encompassing fundamental theoretical approaches, practical experimental projects, and commercial application systems for computation, communication and storage.