A short introduction to periodic bandstructure methods suitable for the calculation of Mossbauer parameters is presented. These methods are based on density functional theory (because we want to treat big and complicated systems) and must be accurate not only in the bonding region (like pseudopotential approaches), but also near the atomic nuclei since Mossbauer parameters depend crucially on the wave functions at/near the nucleus. A numerical basis set as in augmented plane wave (APW) based methods is very well suited for this purpose and the APW method is briefly sketched. The results for Y BaFe2O5 are discussed in more detail and compared with experiment.