Recent advances in the theory of X-ray absorption fine structure (XAFS) are reviewed. Modern ab initio multiple-scattering (MS) calculations now provide an accurate, unified treatment of XAFS, encompassing both EXAFS (extended-XAFS), NEXAFS (near-edge XAFS) and XANES (X-ray absorption near-edge structure). Combined with multi-path analysis techniques, such calculations now permit accurate structural determinations well beyond the first near-neighbor. These calculations also describe near-edge features such as sigma* shape resonances and white lines. Implications for catalyst research are briefly discussed.