The pretrial population—the number of people who are detained while awaiting trial—increased 433 percent between 1970 and 2015. This growth is in large part due to the increased use of monetary bail. But pretrial detention has far-reaching negative consequences. This evidence brief presents information on the way that pretrial detention is currently used and summarizes research on its impacts. These studies call into question whether pretrial detention improves court appearance rates, suggests that people who are detained are more likely to be convicted and to receive harsher sentences, and indicate that even short periods of detention may make people more likely to become involved with the criminal justice system again in the future. The brief concludes by highlighting strategies that some jurisdictions have employed to reduce the use of monetary bail and increase pretrial release.