Epistemic trust in others frequently cannot be disentangled from interpersonal trust more generally, but the epistemic implications of how we affectively express our trust in others are under-investigated. This essay claims that gratitude, despite its empirically undeniable importance to human flourishing generally, is also important epistemically and in several intersecting ways. To be grateful to a person is to represent the world differently in key respects. Gratitude, even if it is for past non-epistemic benefits, should play an important role in (...) shaping who we epistemically rely on. Gratitude for specifically epistemic benefits is an important way in which we show our attunement to epistemic value and contribute to the incentive structures that make much of our public knowledge and informational ecosystems possible. Likewise, ingratitude is a crippling epistemic vice that renders our dependence on quality sources of information fragile and vulnerable to capture by misinformation. (shrink)