Abstract. Experimental investigations on protein dynamics are usually carried out in solution; however, in most cases, the determination of protein structure is done by crystallography that relies on the diffraction properties of the protein arranged in a three-dimensional lattice. X-ray Absorption Spectroscopy (XAS) is an ideal tool to investigate the deep relationships between structure and dynamics, on a wide class of metal containing proteins, including hemeproteins. In fact, this technique can be used either as a structural refinement of X-ray diffraction on the same crystal, or as an independent tool to study structural dynamic properties both in crystal and solution. Different examples will be presented and discussed, with particular emphasis onto the original contribution due to the application of the MXAN software package to the analysis of XANES spectra.