I will show how synchronization subserves selective visual attention. We find that natural viewing induces pronounced gamma-band synchronization in early visual areas. Very similar gamma-band synchronization is induced during controlled visual stimulation and attentional selection. Under those conditions, we find that only the gamma rhythm induced by the behaviorally relevant, attended, stimulus synchronizes to higher visual areas. We propose that this selective inter-areal gamma-band synchronization subserves the selective routing of attended signals. We then investigate how this gamma-band synchronization among early and high visual areas is modulated by control areas. We find that posterior parietal cortex exerts beta-band influences onto visual areas, that those are enhanced by attention and that they enhance gamma-band synchronization between visual areas. Looking across 28 pairs of simultaneously recorded visual areas, we find that generally, top-down influences are mediated by beta-band synchronization and bottom-up influences by gamma-band synchronization. Finally, we investigate how attention changes the local synchronization, resolved for cell types, namely putative pyramidal cells and inhibitory interneurons. We find that interneurons gamma-lock twice as strongly as pyramidal cells, and that pyramidal cells precede interneurons by 66 degree in the gamma cycle. During pre-stimulus attentional engagement, pyramidal cells hardly gamma-synchronize, while interneurons gamma-synchronize as strong as when they are visually stimulated. During visual stimulation, selective attention sharpens the gamma-synchronized ensemble in that weakly driven cells become less and strongly driven cells more gamma synchronized. Together, these results show how neuronal synchronization subserves attention at several levels from microcircuits to inter-areal networks.