Delays in clinical deterioration recognition and failures to rescue lead to serious adverse events. Rapid response systems (RRS) have been implemented with the aim of improving the identification and management of clinically worsening hospital ward patients. Although early studies reviewing RRS showed improvements in clinical outcomes, subsequent results have not shown consistent benefit. This review describes RRS, including controversies surrounding them, potential benefits and limitations, as well as strategies to implement them successfully. An AHRQ WebM&M perspective discusses lessons from early experiences with RRS.