Active shooter is a term used by law enforcement to describe a situation in which a shooting is in progress and an aspect of the crime may affect the protocols used in responding to and reacting at the scene of the incident. Unlike a defined crime, such as a murder or mass killing, the active aspect inherently implies that both law enforcement personnel and citizens have the potential to affect the outcome of the event based upon their responses. To provide further clarity on these threats, the Federal Bureau of Investigation (FBI) in 2014 initiated a study of "active shooter" incidents. The goal of the FBI study is to provide federal, state, and local law enforcement with data so they can better understand how to prevent, prepare for, respond to, and recover from these incidents. As a result, the FBI identified 160 active shooter incidents that occurred in the United States between 2000 and 2013. Though additional active shooter incidents may have occurred during this time period, the FBI is confident this research captured the vast majority of incidents falling within the search criteria. To gather information for this study, researchers relied on official police records, FBI records, and open sources. The time span researched was intended to provide substantive results to aid in preparedness and response efforts. This study is not intended to explore all facets of active shooter incidents, but rather is intended to provide a baseline to guide federal, state, tribal, and campus law enforcement along with other first responders, corporations, educators, and the general public to a better understanding of active shooter incidents. [The report was published with Texas State University.]