An efficient representation of the environment requires both the selection of a fraction of the information that reaches our senses and the organization of this information into coherent and meaningful elements. Here we discuss the dynamic interplay between selective attention and perceptual organization, important processes that allow us to perceive a seamless, integrated world. Based on evidence from behavioral and neuroimaging studies with normal observers and neuropsychological patients, we examine whether: perceptual grouping constrains visual attention, determining which objects will be (...) selected and be candidates for explicit report; visual attention modulates perceptual grouping, determining how elements are grouped to form meaningful wholes. The data suggest that, whilst not being necessary for at least some forms of perceptual grouping, visual attention can nevertheless modulate grouping. We conclude that selection is dynamically set by bottom-up stimulus factors, top-down knowledge and the allocation of attention to space and within grouped regions of objects. (shrink)