Protein dynamics reveals the complexity of these biomolecules. The structural fluctuations and relaxations are determined by a rugged energy landscape where the vallies, the conformational substates, are arranged in a hierarchy of tiers. Several experimental techniques have been used to study the different aspects of protein dynamics. We discuss X-ray structure determinations and pressure tuned hole burning experiments to study structural distributions. Equilibrium fluctuations have been studied by Mössbauer spectroscopy, Rayleigh scattering of Mössbauer radiation and incoherent neutron scattering. Most results on structural relaxations have been obtained from the CO rebinding kinetics in CO ligated myoglobin after flash-photolysis. In addition some Mössbauer investigations of structural relaxation are discussed.