The results of an atomistic simulation study on the incorporation of ions of the first series of transition metals (Cr3+, Cr4+, Fe2+, Fe3+, Co2+, Co3+, Ni2+, and Ni3+), Y3+, and ions of the lanthanide series (Er3+, Gd3+, Tb3+, Pr3+, Pr4+, and La3+) in the BaTiO3 lattice are presented and discussed. The ions of the transition metals prefer to substitute at the titanium site with oxygen-vacancy compensation. For iron and cobalt, oxidation from the divalent to the trivalent state during incorporation is favored. Nickel and chromium are preferentially incorporated in the valence state 2+ and 3+, respectively. Formation of stable defect pairs with different types of lattice defects is predicted for the transition-metal impurities, For La3+ and Pr3+, substitution occurs at the barium site, whereas Y3+, Tb3+, Gd3+, and Er3+ tend to simultaneous substitution on both cation sites. Formation of dopant-titanium-vacancy pairs is predicted for the rare earth ions and Y3+. The effect of doping on the lattice parameter of c-BaTiO3 has been studied by a mean-field calculation Comparison with experimental data confirms the dependence of the preferred substitution site on the ionic radius of the impurity. For dopants with intermediate size (Y3+, Er3+, Tb3+, and Gd3+), the Ba/Ti ratio is important in the incorporation mechanism.