People's decisions and judgments are disproportionately swayed by improbable but extreme eventualities, such as terrorism, that come to mind easily. This article explores whether such availability biases can be reconciled with rational information processing by taking into account the fact that decisionmakers value their time and have limited cognitive resources. Our analysis suggests that to make optimal use of their finite time decision-makers should over-represent the most important potential consequences relative to less important, put potentially more probable, outcomes. To evaluate this account we derive and test a model we call utility-weighted sampling. Utility-weighted sampling estimates the expected utility of potential actions by simulating their outcomes. Critically, outcomes with more extreme utilities have a higher probability of being simulated. We demonstrate that this model can explain not only people's availability bias in judging the frequency of extreme events but also a wide range of cognitive biases in decisions from experience, decisions from description, and memory recall. Keywords: judgment and decision-making; bounded rationality; cognitive biases; heuristics; probabilistic models of cognition Human judgment and decision making have been found to systematically violate the axioms of logic, probability theory, and expected utility theory (Tversky & Kahneman, 1974). These violations are known as cognitive biases and are assumed to result from people's use of heuristics -simple and efficient cognitive strategies that work well for certain A preliminary version of our simulations of decisions from description was presented at the 36th Annual Meeting of the Cognitive Science Society and appeared in the conference proceedings. This work has been updated and extended for inclusion in the current manuscript.We are grateful to Sam Gershman, Elliot Ludvig, Christopher Madan, Marta Kryven, Ido Erev, Nisheeth Srivastava, Thomas Icard, and Phoebe Lin for their helpful pointers, discussion, and assistance.OVER-REPRESENTATION OF EXTREME EVENTS 2 problems but fail on others. While some have interpreted the abundance of cognitive biases as a sign that people are fundamentally irrational (Ariely, 2009;Marcus, 2009;Sutherland, 1992;McRaney, 2011) others have argued that people appear irrational only because their reasoning has been evaluated against the wrong normative standards (Oaksford & Chater, 2007), that the heuristics giving rise to these biases are rational given the structure of the environment (Simon, 1956;Todd & Gigerenzer, 2012), or that the mind makes rational use of limited cognitive resources (Simon, 1956;Griffiths, Lieder, & Goodman, 2015;Wiederholt, 2010;Dickhaut, Rustichini, & Smith, 2009).One of the first biases interpreted as evidence against human rationality is the availability bias (Tversky & Kahneman, 1973): people overestimate the probability of events that come to mind easily. This bias violates the axioms of probability theory. It leads people to overestimate the frequen...