Impairments in attentional control have been associated with a range of psychiatric disorders, such as depression, anxiety, and obsessive-compulsive disorder. The Attention Control Scale (ACS-20) is a measure of attentional control that is widely used due to its clinical and heuristic utility. The ACS-20 consists of 20 items with a 4-point Likert scale. Several studies have found that it is a reliable and valid scale. The initial psychometric evaluation concluded that the ACS-20 is best interpreted as having three factors, namely, focusing, shifting, and flexible thought control. However, subsequent independent evaluations have demonstrated that the ACS has a two-factor structure, namely, Attentional Focusing (9 items) and Attentional Shifting (11 items). Independent studies have found supporting evidence for the internal consistency and discriminant validity of the scale versions across a range of samples. The ACS-20 has been translated into various languages including French, German, Persian, Polish, and Slovak with satisfactory internal consistency and discriminant validity. Additional research using performance-based tasks or physiological tasks is warranted to verify the scale’s convergent and predictive validity. Notable limitations of ACS include the bias associated with the self-reported nature of the ACS and aspects related to design and analysis of validation studies reporting on its psychometric properties.