We live in an uncertain social world. For many people, the future feels, and frequently is, indeterminant. Climate change, technological change, demographic change, and cultural change all make it difficult to tell where society is headed. Since it is our collective actions which will shape society’s future, it is more important than ever to reflect on the nature of uncertainty and its impacts on those actions. How exactly does uncertainty impact action? In particular, how does uncertainty about society's future bear upon risk-mitigating collective action? Knight (1921) defined “uncertainty” as a state in which one does not know, does not know what one does not know, and may not even know that one does not know. Uncertainty therefore presents a challenge for rational action because it suggests there are many situations in which an informed decision is impossible. “Preppers” are a growing lifestyle movement and subculture who believe that major disasters are unavoidable, and that the world as we know it will end soon. Preppers spend impressive amounts of time, money, and energy attempting to mitigate these imagined risks. They learn about various disasters, stockpile large amounts of supplies, buy specialized gear, and learn numerous survival “skillsets.” Preppers go to great lengths to prepare for disasters that most of us don’t even consider. Therefore, preppers offer a strategic case for unpacking the mechanisms through which societal uncertainty is translated into collective action. Preppers force us to attend to: a) the prevalence, scope, and interconnectedness of real, present-day, society-threatening uncertainties, and b) the way social and cultural forces clearly shape representations of society’s future. Drawing on 5 years of participant observation with preppers in Southern California and on YouTube, I argue that preppers imagine future disasters in order to reconstruct uncertainty into risks to be avoided. In doing so, they make lines of seemingly rational action apparent. In other words, uncertainty requires preppers to use their imaginations, social interactions, and pieces of culture to make mental representations of an unknown future. This means professedly rational decisions are invariably embedded in webs of social status and cultural and moral significance. I explore this more fully in chapter one, which draws on my fieldwork with preppers during the Covid-19 pandemic to discuss the relationship between uncertainty, risk, and rationality. In chapter two, I give an overview of my methods and apply the theoretical framework from chapter one to ethnographic research. I argue that ethnography, like prepping, is characterized by considerable uncertainty, and that ethnographers appear to respond to uncertainty using the same process. In chapter three, I ask what forces shape preppers’ assessments of the risks. I argue that while preppers’ fears are often valid, both their perceptions of and their responses to risks are shaped by moral and cultural, as opposed to merely instrumental, scripts. In chapter four, I examine how preppers’ economic actions are guided by the ways in which they imagine future disasters, and by the values they assign to money. This suggests that even risk-mitigating economic action is still embedded in culture. In chapter five, I explore the discursive strategies preppers use to legitimate their expert claims about the future. I show that both the rationalist and realist discourses in which preppers ground their claims, hinge on performances of masculinity. This suggests that not only culture, but also social structure, shape actions through uncertainty. Preppers direct our attention to the way uncertainty complicates both individual rational action and historical rationalization. By all accounts, risk-mitigating action should be rational. Yet by taking seemingly rational action to extremes, preppers help to expose rationality’s underlying contractedness. My analysis suggests that social representations and imaginaries are a crucial area in which this social construction takes place, as situated historical actors project their own backgrounds, social locations, and culture into the future. By highlighting the social and cultural forces constructing rational action, this dissertation calls into question rationality’s objective (as opposed to merely normative or discursive) basis.