Electron correlations in atoms or atomic ions with multiple electrons are discussed extensively. The scheme of correlations between the electronic configurations are investigated in view of the (Dirac)-Hartree-Fock type variational calculations. In highly lying states realized by multiple inner-shell electron excitations, single electron orbitals have to be modified in accordance with the creation of electron vacancies near the atomic centre; the optimizatons of orbitals for individual energy levels are indispensable to gain a good insight of such atomic states and their dynamics. Electronic configurations with the same total parities may interact each other even in the cases that the constituent single electron orbitals have opposit parities. Such configuration interactions may induce the hybridization of single electron orbitals providing us with characteristic interference structures in the optical emission or absorption spectra. Numerical examples have been illustrated for several atomic or ionic systems such as lithium hollow atomic states, neon core excited states, and 4d-open highly charged tin ionic states.