The purpose of this study was to test the hypothesis that the dorsolateral prefrontal cortex (DLFPC), not the anterior cingulate cortex (ACC), plays the predominant role in implementing top-down attentional control. To do so, we used fMRI to examine practice-related changes in neural activity during a variant of the Stroop task. The results indicated that the DLPFC's activity decreased gradually as the need for control was reduced (as indexed by behavioral measures), while the ACC's activity dropped off rapidly. Such a pattern is consistent with the DLPFC taking a leading role in implementing top-down attentional control and the ACC being involved in other aspects of attentional control, such as response-related processes. In addition, with practice, there was a reduction in activity within cortical systems handling the processing of task-irrelevant information capable of interfering with task performance. This finding suggests that with practice the brain is capable of identifying and strategically inhibiting such processing.