The electronic and spatial structures of the La impurity in BaF2 are investigated using the ab initio method of linear combinations of atomic orbitals based on the Hartree-Fock approximation in the supercell model. Calculations are performed using the CRYSTAL-98 software package. Possible models of defects are discussed. The MOLSTAT computer code is employed to estimate the energies of formation of defects and their parameters. The influence of defects on the BaF2 band structure is analyzed.