Oppositional Defiant Disorder (ODD) is a type of behavior disorder. Children with ODD are uncooperative, defiant, and hostile toward peers, parents, teachers, and other authority figures. Developmental problems may cause ODD. Or the behaviors may be learned. Oppositional defiant disorder (ODD) is a type of childhood disruptive behavior disorder that primarily involves problems with the self-control of emotions and behaviors. According to the Diagnostic and Statistical Manual of Mental Disorders, Fifth Edition (DSM-5), the main feature of ODD is a persistent pattern of angry or irritable mood, argumentative or defiant behavior, or vindictiveness toward others. However, several issues, such as symptom threshold, dimensional versus categorical conceptualization, and sex-specific symptoms, are yet to be addressed. Although ODD was found to be highly heritable, no genetic polymorphism has been identified with confidence. There has been a definite genetic overlap with other externalizing disorders. Studies have begun to explore its epigenetics and gene–environment interaction. Neuroimaging findings converge to implicate various parts of the prefrontal cortex, amygdala, and insula. Alteration in cortisol levels has also been demonstrated consistently. Although a range of environmental factors, both familial and extrafamilial, have been studied in the past, current research has combined these with other biological parameters. Assessment and treatment decisions are also complicated by the introduction of disruptive mood dysregulation disorder, which markedly overlaps with the irritability dimension of ODD. Effective treatments for ODD are well established, but suffer from confounding with age and behavioral severity, such that fewer validated treatments are available for older individuals with ODD who do not develop conduct disorder. This is particularly true regarding the treatment of adult ODD, which has received almost no attention. Established treatments for ODD may also not give sufficient attention to irritability as a distinct aspect of the disorder.