This study describes how organizations respond to signs that may or may not portend future catastrophes. The authors examine the space shuttle Columbia disaster in depth, with particular attention to the group dynamics and organizational cultural barriers that combined to produce an ineffective response to the "ambiguous threat" posed by the foam damage to the shuttle's wing. Examples from health care, such as the deployment of rapid response teams, are used to illustrate how recognizing early signals, practicing teamwork, and encouraging experimentation can prevent ambiguous threats from developing into substantive threats. Bohmer and Edmondson have previously described the collective learning process that health care organizations should strive to achieve.