Individual differences in the ability to control attention are correlated with a wide range of important outcomes, from academic achievement and job performance to health behaviors and emotion regulation. Nevertheless, the theoretical nature of attention control as a cognitive construct has been the subject of heated debate, spurred on by psychometric issues that have stymied efforts to reliably measure differences in the ability to control attention. For theory to advance, our measures must improve. We introduce three efficient, reliable, and valid tests of attention control that each take less than 3 min to administer; Stroop Squared, Flanker Squared, and Simon Squared. Two studies (online and in-lab) comprising more than 600 participants demonstrate that the three “Squared” tasks have great internal consistency (avg. = .95) and test–retest reliability across sessions (avg. r = .67). Latent variable analyses revealed that the Squared tasks loaded highly on a common factor (avg. loading = .70), which was strongly correlated with an attention control factor based on established measures (avg. r = .81). Moreover, attention control correlated strongly with fluid intelligence, working memory capacity, and processing speed and helped explain their covariation. We found that the Squared attention control tasks accounted for 75 percent of the variance in multitasking ability at the latent level, and that fluid intelligence, attention control, and processing speed fully accounted for individual differences in multitasking ability. Our results suggest that Stroop Squared, Flanker Squared, and Simon Squared are reliable and valid measures of attention control.