The additive overlap populations of atomic orbitals ξ_ab = Re(S_ab(PS)_ba) and Ξ_ab = ξ_ab + ξ_ba , relating McWeeny's and Mulliken's additive populations of AO n^M_a = Re(PS)_aa with Davidson's total electron populations n_a= (SPS)_aa , are suggested for a quantum chemical description of the electronic structure of molecules and crystals. The theory is illustrated by an electron population analysis for HCN , N2 , F2 , and B₂H₆ molecules.