We used the combination of functional magnetic resonance imaging and event-related potentials to decompose the processing stages ( mental chronometry) of working memory retrieval. Our results reveal an early transient activation of inferotemporal cortex, which was accompanied by the onset of a sustained activation of posterior parietal cortex. We furthermore observed late transient responses in ventrolateral prefrontal cortex and late sustained activity in medial frontal and premotor areas. We propose that these neural signatures reflect the cognitive stages of task processing, perceptual evaluation ( inferotemporal cortex), storage buffer operations ( posterior parietal cortex), active retrieval ( ventrolateral prefrontal cortex), and action selection ( medial frontal and premotor cortex). This is also supported by their differential temporal contribution to specific subcomponents of the P300 cognitive potential.