Disruptive mood dysregulation disorder (DMDD) is characterized by a chronic and persistent angry or irritable mood and recurrent temper outbursts. The addition of DMDD as a diagnostic category was one of the most significant and controversial changes in the Diagnostic and Statistical Manual for Mental Disorders, Fifth Edition (DSM-5), which was published in 2013. This entry describes the diagnostic criteria for DMDD, its prevalence in the general population, information related to etiology and symptom course, impact on caregivers, and proposed treatments worthy of future investigation.