A “sentinel event” is a negative outcome that signals underlying weaknesses in a system or process; is likely the result of compound errors; and may, if properly understood, provide important keys to strengthening the system and preventing similar adverse outcomes in the future. The U.S. Justice Department’s National Institute of Justice (NIJ) is currently mobilizing sentinel-event review (SER) to be a routine, culture-changing practice that can lead to increased system reliability and greater public confidence in a system’s legitimacy. In 2014, NIJ asked jurisdictions from around the Nation to volunteer for an experiment (“beta test”) of the SER process. A competitive process was used in selecting three cities to participate - Milwaukee, Philadelphia, and Baltimore. Although each site yielded important differences in how the SER team was structured and how they conducted their SER, at this point, there is no single structure for a successful SER in the criminal justice system. The current report is a guide to questions that jurisdictions should ask and factors they should consider in designing an SER. Subsequent research efforts will examine the sustainability of the SER process in criminal justice and the extent to which it achieves measurable public safety and system improvements. The issues addressed in this report are where and how to start a SER; how to choose the “right” event for SER; who should be on the SER team; who should lead the SER; the role of a researcher in SER; how to structure the SER and set ground rules; the meaning of a “non-blaming” review; dealing with data-sharing issues; where challenges will likely arise; what happens when an SER is complete; and how a jurisdiction can sustain SER.