The Apathy Evaluation Scale (AES) is a tool utilized with individuals with brain injury, neurocognitive disorders, and other mixed populations to quantify and characterize apathy in adults. The scale "treats apathy as a psychological dimension defined by simultaneous deficits in the overt behavioral, cognitive, and emotional concomitants of goal-directed behavior." It has three versions: self-rated (AES-S), clinician-rated (AES-C), and informant-rated (AES-I). Using factor analysis, Marin and colleagues identified three factors for the scale, including general apathy, disinterest or amotivation, and lack of concern. The psychometric properties of the AES have been examined in various clinical cohorts, including individuals with Alzheimer's disease (AD), traumatic brain injury (TBI), acquired brain injury, multiple sclerosis, severe mental illness, and cognitively healthy middle-aged cohort who are at risk for AD. The AES is a useful, reliable, and valid instrument to quantify and measure severity of apathy symptoms in adults. It is important to note that the AES-C and AES-S were able to discriminate apathy from depression and anxiety better than the AES-I did. It has been translated into Japanese, Portuguese, German, and Turkish. As a neuropsychiatric symptom, apathy should be measured in examining problems of relevance to psychology, psychiatry, and neurology, which may aid in understanding motivation, prognosis, and differential diagnosis. (PsycInfo Database Record (c) 2020 APA, all rights reserved).