Serious incidents in the 1970s and continuous growth of factories producing and/or using hazardous substances formed the basis of a quantitative approach to risk. While discussions of risk were conducted in all industrialised countries they were particularly important in The Netherlands due to space limitations and short distances between industrial plants and residential areas. This article is part of a series covering the history of the safety science discipline (Swuste et al., 2015; Van Gulijk et al., 2009; Swuste et al., 2010). The concept risk entered the Dutch safety domain before the 1970s in relatively isolated case studies and in managing flood defences in The Netherlands. Since the 1970s these case studies paved the way for the development of mathematical models for quantitative risk analysis that were based on experience from nuclear power plants, the process industries and reliability engineering from operations research. 'External safety' was a focal point for these early developments in the process industries: adverse effects of dangerous goods outside the factory's property boundaries. The models were documented in standardised textbooks for risk analysis in The Netherlands, the so-called 'coloured books'. These works contributed to the development of the Seveso Directive. For internal safety (taking place within property boundaries) semi-quantitative approaches were developed simultaneously. The models for quantitative risk analysis were deemed reliable, but the acceptability of a quantified risk was another matter. Making decisions on risk relates to complex societal issues, such as ethics, stakeholder perception of risks, stakeholder involvement, and politics, all of which made the decision making process far from straightforward. With the introduction of the abstract concept of risk in the Dutch safety science domain, the question of risk perception became important in Dutch safety research. The concept risk and methods for quantitative risk analysis first entered into Dutch law in environmental risk regulations. It took a while for risk to be accepted by occupational safety experts, but just before the turn of the century 'occupational risk inventory and evaluations' or RI&E methods were introduced into Dutch occupational safety legislation. This finalised the paradigm shift to risk-based safety-decision making in the Dutch safety science domain. While methods for quantifying risk are now widely applied and accepted, the proper use of risk perception and risk in the political decision process are still being debated.