In five studies with overlapping designs and intents, subjects predicted a specific peer's responses to a variety of stimulus situations, each of which offered a pair of mutually exclusive and exhaustive response alternatives. Each prediction was accompanied by a subjective probability estimate reflecting the subjects' confidence in its accuracy—a measure validated in Study 5 by having subjects choose whether to “gamble” on the accuracy of their prediction or on the outcome of a simple aleatory event. Our primary finding was that in social prediction, as in other judgmental domains, subjects consistently proved to be highly overconfident. That is, regardless of the type of prediction item (eg, responses to hypothetical dilemmas, responses to contrived laboratory situations, or self-reports of everyday behaviors) and regardless of the type of information available about the person whose responses they were predicting (eg, predictions about roommates or predictions based on prior interviews), the levels of accuracy subjects achieved fell considerably below the levels required to justify their confidence levels. Further analysis revealed two specific sources of overconfidence. First, subjects generally were overconfident to the extent they were highly confident. Second, subjects were most likely to be overconfident when they knowingly or unknowingly made predictions that ran counter to the relevant response base rates and, as a consequence, achieved low accuracy rates that their confidence estimates failed to anticipate. Theoretical and normative implications are discussed and proposals for subsequent research offered.