Serious and undesirable events in health care organizations should trigger analysis and response to minimize the risk of recurrence. Sentinel Events: Evaluating Cause and Planning Improvement, a new book from the Joint Commission, describes the types of errors and sentinel events that have been reported in health care organizations, how organizations can respond to these events, how sentinel events are investigated through root cause analysis, and the Joint Commission's policy on sentinel events. Several case studies and examples demonstrate successful event investigation and improvement efforts in health care organizations. This excerpt addresses prevention of sentinel events through proactive, risk-reduction approaches. It is our hope that, even without the stimulus of a sentinel event, organizations will embrace the concept of prospective design and analysis of health care processes and systems to minimize the possibility of errors and to protect patients from the effects of errors that do occur.