Adversarial legal procedure is one of the defining features of the American legal system. Adversarialism has long been criticized for breeding a combative style of lawyering that precipitates a host of injurious effects that outweigh its virtues. Seeking to explore the psychological foundations of this combat model, this article suggests that playing an adversarial role skews legal actors’ views of their case toward greater congruence with that role. This expansive bias encompasses distortions of interpretations of evidence, beliefs, and judgments, and it results in corresponding motivations, emotions, and more. The article discusses three facets of the legal process that illustrate the harms wrought by the combat model and its underlying adversarial bias. The persistence of the combat model is a testament to adversarialism’s iron grip on the American legal imagination.