Risks are of particular relevance for the social history of the twentieth century. On the one hand, Western societies’ economic growth gave impetus to the rise of new technologies. Technology, we argue, brought with it new possibilities, but it was also loaded with new risks. On the other hand, societies discussed and explored new notions of responsibility for risks, their management and mitigation. Both aspects changed the meaning and perception of traditional risks, such as natural catastrophes, sickness or falling into poverty. In this introduction, we explore the use of risk as a category of analysis for a social history of the twentieth century. In a form of double-intervention on time and methodology, we, on the one hand, hold risks as a ‘phenomenon’ to be of particular relevance – even characteristic for – the twentieth century; on the other hand, we posit that risk as an analytical category offers us new avenues into understanding modern societies in three important ways: (1) the importance of time and future in human actions and debates, (2) the dual nature of risks as discursively constructed and simultaneously material, (3) the social justice implications of this dual nature that were often unequally shared, be it nationally or globally. In the end, we argue, by linking the materiality of challenges and risks with how these were perceived and discursively constructed, we are better able to understand the rules and the changes that underpin historical societies and which are – as our authors show in this HSR Special Issue – very often determined in reaction to risks.