Chapter 5 explains how the human became increasingly acknowledged to be a recipient of safety trouble—trouble that was created upstream and then handed down to them by their tools, technologies, organizations, working environments or tasks. Human factors was a field that grew from the insights of engineering psychologists in the 1940s. Confronted with the role of the human in increasingly complex technological systems, it represented an important hinge in this thinking about the relationship between humans, systems, and safety. Systems and technologies were considered malleable, and they should be adapted to human strengths and limitations. Indeed, individual differences were less important than devising technologies and systems that would resist or tolerate the actions of individuals, independent of their differences. Safety problems had to be addressed by controlling the technology. The approach of human factors led to a rekindling of our interest in mental and social phenomena. These became important for understanding how best to design and engineer technologies that fit the strengths and limitations of human perception, memory, attention, collaboration, communication, and decision-making. A few decades later, the field departed from an overly technicalized, individualist, laboratorytask-based, and mentalist information processing paradigm and took the study of cognition ‘into the wild’ to understand people’s collaborative sensemaking in their interaction with actual complex, safety-critical technologies. It led to an entirely new take on human factors, in the field known as cognitive systems engineering.