School tip lines, which are structured systems that allow students, parents, school staff, or community members to report information about potential threats, are a promising approach to school safety. Tip lines, which focus on preventing incidents that are threats to school safety or student well-being, come in various forms, including computer applications, Web sites, and telephone hotlines. Studies have shown that, in many school shooting incidents and other attacks, there were warning signs known to other individuals before the act was carried out. Leveraging such knowledge about potential threats, tip line systems relay information to the most appropriate parties, such as school officials, law enforcement officers, and mental health professionals, so action can be taken before an incident occurs. Although tip lines are promising, very little is known about how widely they have been implemented and what their characteristics are. This report is based on survey responses from a nationally representative sample of 1,226 school principals conducted from February through July 2019. The survey, conducted by RTI International, an independent, nonprofit research institution, was designed to document the prevalence of tip lines, types of schools that are more likely to use tip lines, ways in which tip lines are designed and implemented, challenges of operating tip lines, and perceived effectiveness of tip lines.