Assigning meaning to words, sounds, and objects requires stored conceptual knowledge plus executive mechanisms that shape semantic retrieval according to the task or context. Despite the essential role of control in semantic cognition, its neural basis remains unclear. Neuroimaging and patient research has emphasized the importance of left inferior frontal gyrus (IFG)-however, impaired semantic control can also follow left temporoparietal lesions, suggesting that this function may be underpinned by a large-scale cortical network. We used repetitive transcranial magnetic stimulation in healthy volunteers to disrupt processing within 2 potential sites in this network-IFG and posterior middle temporal cortex. Stimulation of both sites selectively disrupted executively demanding semantic judgments: semantic decisions based on strong automatic associations were unaffected. Performance was also unchanged in nonsemantic tasks-irrespective of their executive demands-and following stimulation of a control site. These results reveal that an extended network of prefrontal and posterior temporal regions underpins semantic control. © The Author 2010. Published by Oxford University Press. All rights reserved.