At their arrival in North America, travelers from the Old Continent were exposed to a radically different civilization. Among the many practices that captured their imagination was scalp-taking. During a battle, the Native American warrior would often stop after having killed or subdued the enemy and cut off his scalp. In this article, we develop an economic theory of this gruesome practice. We argue that scalp-taking constituted an institutional solution to the problem of monitoring warriors’ behavior in the battlefield under conditions of high information costs.