The nuclei in the center of atoms undergoing spin crossover can serve as spectators which via their emitted radiation provide information about the microscopic mechanisms governing the process. Conventional Mössbauer spectroscopy has proven its usefulness in this respect. Application of nuclear resonant scattering of synchrotron radiation opens new possibilities in various ways: Nuclear resonant forward scattering (NFS) makes studies of very small samples, e.g., in pressure cells or as single crystals, feasible and yields results of the Lamb-Mössbauer factors with high accuracy, while nuclear inelastic scattering (NIS) has initiated a novel field of vibrational spectroscopy. Examples and results of these methods will be given in the following chapter.