In this study, measures of irrational beliefs based on the principles of Rational Emotive Behavior Therapy (REBT) were reviewed and contrasted based on psychometric characteristics and quality of guidelines for interpretation. The use of measures of irrational beliefs is an important component of the assessment of presenting problems in psychotherapy and may inform clinical decision making. Additionally, these measures are a helpful way to identify change in irrational beliefs and to measure the effectiveness of specific interventions to facilitate such change. While there are a number of measures of beliefs, there is considerable variability in their psychometric properties and utility for assessment. The majority of the tests are not produced by a publishing company, nor do they provide test manuals. The reliability and validity evidence presented in the publications varies considerably as do the size and quality of standardization samples, which impacts upon the ability to draw normative conclusions. Analyses demonstrated that most measures of irrational beliefs do not provide the evidence needed to adequately address the Standards for Educational and Psychological Testing (Standards; American Educational Research Association [AERA], American Psychological Association [APA], National Council on Measurement in Education [NCME] 1999). Discussion of the implications of this review for the development of future measures of irrational thinking by researchers as well as recommendations in the test selection process for an REBT practitioner is offered.