Episodic memory facilitates flexible decision-making via access to detailed events.

Our experiences contain countless details that may be important in the future, yet we rarely know which will matter and which will not. This uncertainty poses a difficult challenge for adaptive decision-making, as failing to preserve relevant information can prevent us from making good choices later on. One solution to this challenge is to store detailed memories of individual experiences that can be flexibly accessed whenever their details become relevant. By allowing us to store and recall specific events in vivid detail, the human episodic memory system provides exactly this capacity. Yet, whether and how this ability supports adaptive behaviour is poorly understood. Here we aimed to determine whether people use detailed episodic memories to make decisions when future task demands are uncertain. We hypothesized that the episodic memory system's ability to store events in great detail allows us to reference any of these details if they later become relevant. We tested this hypothesis using a novel decision-making task in which participants encoded individual events with multiple features and later made decisions based on these features to maximize their earnings. Across 5 experiments (total n = 535), we found that participants referenced episodic memories during decisions in feature-rich environments and that they did so specifically when it was unclear at encoding which features would be needed in the future. Overall, these findings reveal a fundamental adaptive function of episodic memory, showing how its rich representational capacity enables flexible decision-making under uncertainty.