Working memory, the short-term maintenance and manipulation of information, relies strongly on neural activity in the frontal cortex. Understanding the functional role of this activity is a prerequisite for the understanding of cognitive control mechanisms. Functional imaging studies in human participants have attempted to reveal neural correlates of the subdivision of visual working memory into different processes ( maintenance vs manipulation) and according to the type of memorized content. Here, we show, using functional magnetic resonance imaging, a content-specific dissociation of frontal activity, with dorsal premotor areas supporting both maintenance and manipulation of spatial features and more ventral areas supporting maintenance and manipulation of color. Manipulation- specific activity was observed in the anterior middle frontal gyrus, the inferior frontal junction, and the inferior parietal lobe bilaterally. These areas have been implicated in cognitive control, and their activation by the manipulation task conforms to the demand on central executive resources in this condition. We suggest that the enhanced demand on cognitive resources in manipulation compared with maintenance was met by interplay of content- and task- specific modules in a frontoparietal network.