Safety has traditionally been defined as a condition where the number of adverse outcomes was as low as
possible (Safety-I). From a Safety-I perspective, the purpose of safety management is to make sure that the
number of accidents and incidents is kept as low as is reasonably practicable. Safety management must start
from the manifestations of the absence of safety and that – paradoxically – safety is measured by counting the
number of cases where it fails rather than by the number of cases where it succeeds. This unavoidably leads to
a reactive approach based on responding to what goes wrong or what is identified as a risk.

Focusing on what goes well, rather than on what goes wrong, changes the definition of safety from ‘avoiding
that something goes wrong’ to ‘ensuring that everything goes well’. More precisely, Safety-II is the ability to
succeed under varying conditions, so that the number of intended and acceptable outcomes is as high as
possible. From a Safety-II perspective, the purpose of safety management is to ensure that as much as possible
goes well, in the sense that everyday work achieves its objectives. This means that safety is managed by what
it achieves, and is measured by counting the number of cases where things go well. In order to do this, safety
management cannot only be reactive, it must also be proactive. But it must be proactive with regard to how
actions succeed, to everyday acceptable performance, rather than with regard to how they can fail.

This book analyses and explains the principles behind both approaches and uses this to consider the past and future of safety management practices. The analysis makes use of common examples and cases from domains such as aviation, nuclear power production, process management and health care. The final chapters explain the theoretical and practical consequences of the new perspective on the level of day-to-day operations as well as on the level of strategic management (safety culture).