The Kekulé description of benzene as a mixture of the two structures and was given a firm foundation in quantum theory as a `resonance hybrid' (see, for example, ref. 1). As molecular orbital (MO) theory developed, it was felt that the aromatic character of benzene was explained more naturally in terms of delocalized orbitais. The view that delocalized electrons provide essentially the correct description for this type of system appears to be accepted at all levels2; however, we present here theoretical evidence which challenges this view. We show that the π-electrons in benzene are almost certainly localized and that the characteristic properties of such a system arise from the mode of spin coupling.