Early warning systems (EWS), in the context of secondary transition, are tools that analyze individual student-level data and estimate each student's risk of dropping out of school or completing school on time. Such tools generally consider three primary types of data--commonly referred to as the A, B, Cs: attendance/absence data, behavior/discipline data, and course performance/credit accrual data (Mac Iver & Mac Iver, 2009). Based on the values of variables examined in each of these categories, a student is assigned a numeric score, which is compared to a series of cut points that delimit a series of risk levels (e.g., low, medium, high risk). The focus of the literature addressing EWS is primarily on school completion (i.e., dropout prevention and graduation), rather than on secondary transition per se, and is aimed at practitioners. Many EWS articles address the predictors of success for various grades (Allensworth, Gwynne & de la Torre, 2014) and how EWS can be implemented to identify interventions and supports that will help students remain in school and succeed (Frazelle & Nagel, 2015). This annotated bibliography summarizes various EWS publications according to the type of research (i.e., experimental, correlational, descriptive, discussion, reviews). [This bibliography was originally prepared for the National Technical Assistance Center on Transition (NTACT) in 2016 by Mathew Klare and Bradley Stevenson. It was updated in 2017 by Misty Terrell.]