Twenty Years of School-based Mass Shootings in the United States: Columbine to Santa Fe is an examination of twenty years of school-based mass shootings, from Columbine to Santa Fe, exploring the larger environmental framework within which these incidents occurred. Angelyn Spaulding Flowers and Cotina Lane Pixley use a mixed-methods approach to examine a diverse set of factors, identifying risk and protective factors along with specifically desired public policy responses by evaluating the convergence of variables from the range of school-based mass shootings included in this study. These variables include the type of weapon used, the availability of that type of weapon, perpetrator characteristics, school characteristics, as well as the geospatial and demographic characteristics of the school neighborhood. These school-based mass shooting incidents are explored at both the state and regional level and are further discussed in comparison to leisure time gun use, homicide rates, and suicide rates in the geographical area. The overarching geospatial analytical framework for this research also includes an examination of the manner in which existing policy enactments such as state gun laws vary by geography. Spaulding Flowers and Lane Pixley argue that the increased number of fatalities in school-based mass shooting is largely due to the increased lethality of the weapons, and they propose alternative solutions. Scholars of criminology, sociology, political science, and history will find this book particularly useful.