The school resource officer (SRO) program began in the United States in the early to mid-1950s, however, the program did not gain prominence until the 1990s in response to various school shootings. According to national data, SROs can be found in 35 percent of school across America, regardless of level (elementary, middle, or high school), urbanicity (rural, town, suburban, or city), or enrollment size. However, there is currently a dearth of meaningful research addressing the role and effectiveness of SROs. This article reviews what is known concerning SROs in an effort to establish a foundation for future research centered on the effectiveness of SROs in ensuring students attend safe learning environments. (Contains 1 note.)