Mood swings in children and adolescents have garnered increased interest in recent years. Terms such as emotional lability, affective dysregulation, and mood instability are used to describe a clinical picture that is often characterized not only by sudden and unpredictable negative mood shifts but also by irritability and anger outbursts, a fiery temperament, and low frustration tolerance. The guide outlines the diagnostic and therapeutic approach to this complex disorder. To differentiate commonly occurring normal developmental phenomena, such as defiant behavior, tantrums, and mood swings, from genuinely impairing disorders of affect regulation, the guide provides detailed assistance for diagnostic differentiation after a historical and etiological introduction.