Market exchange and the ideologies that accompany it pervade human social interaction. How does this affect people’s beliefs about themselves, each other, and human nature? Here we describe market cognition as social inferences and behaviors that are intensified by market contexts. We focus on prosociality and two countervailing ways in which market cognition can affect it. On the one hand, marketplaces incentivize individuals to behave prosocially in order to be chosen as exchange partners—thereby generalizing cooperation and trust beyond group boundaries. On the other hand, markets encourage a view of people as self-interested and can thus taint people’s interpretation of prosocial actions and erode more communal forms of cooperation. We close by considering how market cognition can become self-fulfilling, altering relationships, communities, and cultural norms.

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