Protection of Cyber-Physical Systems and Industrial Control Systems (ICS) Bank Of Models: Sensor Attack Detection and Isolation in Industrial Control Systems -- Super Detector: An Ensemble Approach for Anomaly Detection in Industrial Control Systems -- Optimal Man-In-The-Middle Covert Attack -- GNSS Positioning Security: Automatic Anomaly Detection on Reference Stations -- C(I)IP Organisation, (Strategic) Management and Legal Aspects -- Model-Based Risk Analysis Approach for Network Vulnerability and Security of the Critical Railway Infrastructure -- A Survey on Applications of Formal Methods in Analysis of SCADA Systems -- The Cost of Incidents in Essential Services: Data from Swedish NIS Reporting -- Human Factor, Security Awareness and Crisis Management for C(I)IP and Critical Services -- Impact Analysis of PLC Performance when Applying Cyber Security Solutions Using Active Information Gathering -- Multi-Categorical Risk Assessment for Urban Critical Infrastructures -- Use-Case Informed Task Analysis for Secure and Usable Design Solutions in Rail -- Studying Neutrality in Cyber-Space: A Comparative Geographical Analysis of Honeypot Responses -- Future, TechWatch & Forecast for C(I)IP and Critical Services -- Tableau: Future-Proof Zoning for OT Networks -- Link Prediction for Cybersecurity Companies and Technologies: Towards a Survivability Score. .

This book constitutes the refereed proceedings of the 16th International Conference on Critical Information Infrastructures Security, CRITIS 2021, which took place in Lausanne, Switzerland, during September 27-29, 2021. The 12 full papers included in this volume were carefully reviewed and selected from 42 submissions. They were organized in topical sections as follows: protection of cyber-physical systems and industrial control systems (ICS); C(I)IP organization, (strategic) management and legal aspects; human factor, security awareness and crisis management for C(I)IP and critical services; and future, TechWatch and forecast for C(I)IP and critical services.