Special education teachers' (SETs) working conditions play a crucial role in shaping the size, quality, and effectiveness of the U.S. SET workforce and thereby shape the quality of instruction provided to students with disabilities. Valid measures of SETs' working conditions are essential for conducting robust research on how to improve working conditions. We systematically reviewed measures of SETs' working conditions across 44 studies, assessing evidence of validity. We find that evidence of validity for existing measures is limited but that extant measures provide a starting point for future measurement development. We urge researchers to develop valid measures in the future for use in both research and policy aimed at better supporting SETs.