Detection of symmetry—which is abundantly present in the world—is often assumed to be an integral part of the perceptual organization process that is applied to every visual stimulus. On the one hand, as reviewed in this article, the exact role of symmetry in perceptual organization is actually rather elusive due to its interaction with other grouping factors. On the other hand, the detectability of single and multiple symmetry is indeed extraordinary in comparison to that of repetition and Glass patterns. Empirical (...) and theoretical findings pertaining to this detectability are discussed, focusing on converging evidence rather than on details of individual studies, and putting various findings in evolutionary perspectives. Reflecting a seeming opposition between process models and representation models, a specific question is whether symmetry detection relies on crude or precise correspondences between symmetry halves. Both stances find psychophysical support, and this article ends with a unification proposal. (shrink)