This chapter presents landmark findings in each of the three categories of human factors (expertise, situational awareness and teamwork) in the context of cyber security threat detection. It describes from work that expertise in threat detection is a combination of domain and situated knowledge. The chapter shows that how cyber attacks have evolved from conventional scams and isolated denial-of-service and malware attacks launched by independent groups of hackers, to sophisticated attacks that employ a combination of methods launched by nation-state operators and organized cybercrime groups. It also presents the fundamentals, methods, and applications of human factors research in cybersecurity. Operators conducting cyber defense tasks are essential to the analysis of and response to emerging cyber threats. Cognitive task analysis is a common method used in human factors research to represent the cognitive activities and demands of a task, critical decision points, operational policies, strategies, and tools used, both at the individual and team level.