Does making the first offer increase or impair a negotiator's outcomes? Past research has found evidence supporting both claims. To reconcile these contradictory findings, we developed and tested an integrative model — the Information-Anchoring Model of First Offers. The model predicts when and why making the first offer helps versus hurts. We suggest that first offers have 2 effects. First, they serve as anchors that pull final settlements toward the initial first-offer value; this anchor function often produces a first-mover advantage. Second, first offers can convey information on the senders' priorities, which makes the sender vulnerable to exploitation and increases the risk of a first-mover disadvantage. To test this model, 3 experiments manipulated the information that senders communicated in their first offer. When senders did not reveal their priorities, the first-mover advantage was replicated. However, when first offers revealed senders' priorities explicitly, implicitly, or both, a first-mover disadvantage emerged. Negotiators' social value orientation moderated this effect: A first-mover disadvantage occurred when senders faced proself recipients who exploited priority information, but not with prosocial recipients. Moderated mediation analyses supported the model assumptions: Proself recipients used their integrative insight to feign priorities in their low-priority issues and thereby claimed more individual value than senders. The final discussion reviews theoretical and applied implications of the Information-Anchoring Model of First Offers.