The kind of safety work you do depends on what you think is the biggest source of risk. That in turn depends on what your accident model is. Accident models offer ideas about what risk is and how you can best contain it. For the last century or more, a lot of scientific literature has appeared about this. 1 This chapter takes you through four accident models (or, perhaps more correctly, families of models). The next chapter considers the role of the safety department. This role, too, is determined in part by your organization’s ideas about its sources of risk and the nature of accidents.