Mass legal execution is defined as the execution of four or more persons for the same criminal incident by government entities following some form of trial. This study operated under the premise that these executions might reveal more clearly the greatest perceived criminal threats to the society. Mass legal executions were indicative that some crimes were capital offenses in the 18th but not the 20th century. However, for several reasons there is an incomplete record of mass legal execution of African-Americans or anyone else in the United States. This study examined mass legal executions in the United States from the 17th century to the 20th century and what they tell about the social climate of the eras in which they occurred, specifically regarding the place of African-Americans in society. African-Americans were clearly disproportionately involved among those executed, most notably before the formal end of the institution of slavery. Several reasons are presented as to why mass legal executions occurred in the past and why they have ceased to take place in the United States and include: (1) the nature of the offenses; (2) criminals had fewer rights at trials and generally no appeals made it likely that the sentences would be imposed at the same time; and (3) certain crimes were feared by society, particularly slave revolts. What remains today of mass legal executions is the occasional incident of government involved deaths of four or more persons in the process of law enforcement. Appendix, notes, references