Global and local descriptors of chemical reactivity and selectivity are used in order to characterize the nature of the active species of bis(imino)pyridyl iron, a catalyst for olefin polymerization. It is shown that chemical potential, hardness, electrophilicity, as well as the dual and multiphilic descriptors for chemical reactivity and selectivity, are adequate for characterizing the global and local reactivity trends of this organo-metallic complex. Most theoretical evidence presented in this paper indicates that the catalyst of Fe +3 seems to be more active for olefin polymerization than that of Fe +2 . However, when the cocatalyst is considered, catalysts of Fe +2 and Fe +3 present similar electrophilic activity to orientate the nucleophilic attack. It is observed that this activity is well localized at the metallic center in the ferric species whereas it appears to be more delocalized on the ligands of the ferrous species.