“Symmetry” is an extremely broad and versatile concept in physics in general. The realization of symmetries acquires more facets and shadings in quantum theory, than it already exhibits in classical physics. Rather than attempting a full coverage of the topic, I just start by recalling in a schematic way of the richness of the notion in quantum theory, before I turn to a more specific discussion of symmetries in the context of quantum field theory, and finally turn to concentrate on its relation with superselection structure. This relation strongly depends on the number of spacetime dimensions.