 According to an ontological viewpoint, symmetries are seen as a substantial part of the physical world: the symmetries of theories represent properties existing in nature, or characterize the structure of the physical world. It might be claimed that the ontological status of symmetries provides the reason for the methodological success of symmetries in physics. A concrete example is the use of symmetries to predict the existence of new particles. This can happen via the classificatory role, on the grounds of vacant places in symmetry classification schemes, as in the famous case of the 1962 prediction of the particle Omega- in the context of the hadronic classification scheme known as the “Eightfold Way”. (See Bangu, 2008, for a critical analysis of the reasoning leading to this prediction.) Or, as in more recent cases, via the unificatory role: the paradigmatic example is the prediction of the W and Z particles (experimentally found in 1983) in the context of the Glashow-Weinberg-Salam gauge theory proposed in 1967 for the unification of the weak and electromagnetic interactions. These impressive cases of the prediction of new phenomena might then be used to argue for an ontological status for symmetries, via an inference to the best explanation.