Sluggish cognitive tempo (SCT) is characterized by excessive daydreaming, mental confusing and fogginess, and slowed behaviour/thinking. A brief history of the SCT construct is provided, followed by a review of the current research supporting SCT as distinct from ADHD and other psychopathologies. SCT is positively associated with ADHD inattentive symptoms, depression, anxiety, and daytime sleepiness, but is unassociated or negatively associated with externalizing behaviours such as hyperactivity-impulsivity, oppositionality, and aggression. A growing body of research also demonstrates that SCT is uniquely associated with poorer functioning in various domains of major life activities, including academic difficulties (including poor organization, homework problems, and lower grade point average), social problems (especially peer withdrawal and isolation), and emotion dysregulation. SCT is less clearly associated with most neuropsychological performance outcomes with the possible exceptions of sustained attention, processing speed, and motor speed.