Teacher stress, burnout, and attrition are well-documented problems that have been amplified as a result of the COVID-19 pandemic. Recent efforts to study and improve teacher well-being in response to such high levels of burnout are promising. However, the field continues to lack a unified definition of teacher well-being and consistent use of tools with which to measure teacher well-being. These inconsistencies may limit the ability to compare interventions and improve teacher well-being over time. Clarifying how teacher well-being is defined and operationalized can enable others to understand what a particular intervention or study does or does not improve. This systematic review explored 97 studies of teacher well-being and documented tools used to measure the construct. The studies reviewed relied on a wide variety of instruments, ranging from mental health tools to subjective well-being and teacher efficacy measures, with few using specific Teacher Well-Being Scales. Findings suggest the need for more uniform approaches to measurement and the need for a clearly articulated definition of teacher well-being that is distinct from stress or burnout. Researchers recommend the use of a multifactor scale that includes elements of teacher efficacy, school support, workload and time pressure, and job satisfaction.