The processes of photoelectric excitation and subsequent photoelectron scattering are the fundamental building blocks of the X-ray absorption fine-structure (XAFS) phenomenon, being chiefly responsible for the complex material-dependent structure in the X-ray absorption spectrum. Tracking the behaviour of the excited photoelectron is therefore the principal consideration of any XAFS theory, as the XAFS signal itself is facilitated by the elastic scattering of the electron, while the strength of the signal is attenuated by inelastic scattering events. This chapter is chiefly concerned with the quantitative impact of inelastic photoelectron scattering on an XAFS spectrum, and particularly the use of XAFS measurements in deriving experimental values for the electron inelastic mean free path (IMFP), a convenient parameterization of the inelastic scattering cross section for a given electron energy. Here, an overview is provided of the current methods for extracting IMFP data from XAFS, with a discussion of how recent results compare with those of more traditional experimental approaches. The impact of the experimental findings on current understanding of the fundamental theory used to describe low-energy electron transport is dealt with, and subsequent extensions to the quantum dielectric theory of inelastic scattering are discussed.