Air traffic control (ATC) is a cognitively demanding safety-critical activity in which effective performance emerges from the continuous interaction of human cognition, technological systems, operational demands, and organizational conditions. This book provides an integrated examination of the cognitive processes underlying air traffic controller performance and their implications for contemporary and future air traffic management (ATM). Drawing on cognitive psychology, human factors, cognitive systems engineering, and systems safety perspectives, the study synthesizes theoretical and empirical evidence concerning cognitive architecture, situation awareness, decision-making and cognitive biases, mental workload, stress, vigilance, communication, team cognition, and human–automation interaction. Particular attention is given to the transition from individual information-processing accounts toward distributed and socio-technical conceptualizations of controller cognition. The analysis demonstrates that safe ATC performance cannot be attributed to isolated cognitive abilities; rather, it depends on the dynamic construction and maintenance of the traffic picture, adaptive allocation of attentional resources, integration of information across human and technological agents, and flexible regulation of cognitive strategies under changing operational demands. These theoretical arguments are further examined through the 29 January 2025 mid-air collision involving PSA Airlines Flight 5342 and U.S. Army PAT25 near Ronald Reagan Washington National Airport. The case illustrates how workload, attention allocation, situation awareness, expectation-based processing, communication, visual separation, and organizational vulnerabilities may interact across multiple system levels. The book concludes that future ATM should move beyond error-centred approaches and prioritize human-centred automation, cognitive resilience, meaningful human control, and the systematic integration of human performance into system design and safety management.