Background U.S. state legislatures fill a vital role in supporting the use of evidence-based interventions (EBIs) through statutes and regulations (mandates). Objective The study determined the terms used by selected states to describe EBIs and how those terms are defined in mandates. Research Methods The mandates of eight purposely selected states were accessed and coded using the Westlaw Legal Research Database. Results Considerable variation was found in the terms used by states to describe EBIs. Although “evidence-based” was the most frequently utilized term (60% of mandates), an additional 29 alternative terms appeared with varying frequencies. Most terms were simply mentioned, with no further definition or elaboration. When terms were further defined or elaborated, the majority were defined using numerous and different types of external sources or references. Three approaches were found in the mandates defining EBIs: “single definition,” “hierarchies of evidence levels,” and “best available evidence”; the states differed considerably in the approaches used in their mandates. Conclusions The variations in EBI-related terminology across states and within states, coupled with a lack of elaboration on the meaning of important terms and the predominant use of external rather than internal guidelines, may be a source of confusion for behavioral health provider agencies that seek direction about what constitutes an EBI. Prior studies indicate that many agencies may lack staff with the technical ability to adequately evaluate what constitutes an EBI. Thus, lack of clear guidance from official state government mandates may impede the implementation of EBIs within states.