Cognitive control has been defined as the processes underlying goal-directed behavior in the face of distraction. Previous research has highlighted two major difficulties in measuring these processes. First, the measures used to assess cognitive control have been reported to have low reliability (i.e., low correlations between two sessions or between two different halves of the same session). Second, the correlations among different measures of cognitive control have been reported to be low. Together, these difficulties challenge the view that cognitive control or its subprocesses can be measured with several tasks. Critically, these issues have been attributed to methodological issues, such as: (a) the use of difference scores as measures of cognitive control, (b) the difficulty of isolating attentional control from measurement error, and (c) the computation of the cognitive-control measures based on either reaction times or accuracy rates, which neglects individual differences in speed-accuracy trade-offs. Several solutions have been proposed to improve the measurement of cognitive control. The question we face is to what extent these improvements change the validity of the cognitive-control measures. The purpose of this talk is to present the current difficulties in measuring cognitive control. The subsequent talks will explore solutions to the dilemma between reliability and validity in measuring cognitive control.