Several challenges may hinder accurate screening for and assessment of substance use disorders among emerging adults ages 18–29. This chapter discusses emerging adult–specific research on diagnosing substance use disorders and several empirically supported screeners and assessments that may be useful to those working with emerging adults. First, emerging adult–specific research supporting changes to the most recent version of the Diagnostic and Statistical Manual for Mental Disorders, the DSM-5, is reviewed, and nuances in using the DSM-5 with emerging adults are discussed. The chapter highlights idiosyncrasies in emerging adult symptom patterns using data from large national surveys. Finally, a practice-friendly review of screening and assessment instruments commonly used with emerging adults is provided. For screening instruments, administration time, the instrument’s ability to discern which emerging adults exhibit substance use problems, and emerging adult–specific cutoff points in the literature are addressed. For assessment tools, comprehensiveness of the instrument, administration time, and contexts in which the instrument has been used with emerging adults are discussed.