The atomic partition functions of Bi(I), Bi(II) and Bi(III) have been calculated for different values of the reduction of the ionization energy δEi (0.05–2.0 eV) in the temperature range between 2000 and 20 000 K. All parent levels that can be realized under the given physical conditions were considered. For Bi(I) as an example the total partition function was broken down into the separate contributions of various groups of levels and the results for different temperatures and Δei values are brought out and discussed.