This chapter delves into the role of psychological theories in security, with a particular emphasis on the cognitive, social, and emotional factors that influence security behaviour. Cognitive psychology emphasises the impact of cognitive burden, fallacies, and heuristics on risk perception and decision-making. Social psychology investigates the influence of group dynamics, conformity, and diffusion of responsibility on security culture. Compliance with security protocols is influenced by emotional and motivational factors, such as tension and fear-based messaging. Organisations can develop effective security strategies that promote proactive security behaviour, enhance resilience, and mitigate risks by incorporating these psychological perspectives. It is imperative to comprehend these factors in order to enhance security frameworks and mitigate human-related risks in physical and digital security environments.