The objective of the thesis is to present studies addressing the question: How do we identify that a system drifts or experiences sudden changes in the safety space? Hence, the studies in this thesis focus on the identification of safety performance indicators. This identification is influenced by the way safety is understood. If safety is seen as the absence of accidents and failures, then indicators refer to failures, malfunctions or deviations. Safety critical organizations like airlines,

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... navigation service providers or oil companies have implemented numerous improvements by using such lagging indicators. These lagging indicators by their nature provide information after the fact. Nevertheless, today's systems and organizations must be able to function in rapidly changing environments in which there is a great deal of uncertainty. The Resilience Engineering perspective does not see safety as the absence of failures but as something that the organization or the sociotechnical system does. Thus successes and failures are related to the capability of the system or organization to adjust and continue operations in the presence of continuous changes and operational constrains. Given such a perspective, finding indicators that allow an organization to act before something happens, i.e. to be leading, rather than reactive and lagging, is a main challenge.