High energy resolution spectroscopy of energetic (up to 10 keV) Auger and photoelectrons excited by hard (2-10 keV) X-rays from clusters, nanostructures, surfaces, and interfaces of materials with high practical importance has started enjoying an increasing interest recently. The fast development of experimental technique and theoretical models in these days provides a possibility for a very detailed study of electronic structures of such systems including effects of solid environment on atomic transitions. Observing high-energy photoinduced electrons, surface effects on the spectra can be minimized, and the information depth is typically in the order of several times 10 nm, ensuring a new insight into the structure of "buried" interfaces, the local electronic structure surrounding atomic components of key functional importance, or the charge transfer between alloy components. Combining high energy resolution electron spectroscopies using hard X-rays and energetic electrons for excitation of Auger or photoelectrons and backscattered electrons, as well as suitable models (including cluster molecular orbital type) for describing localized and collective electronic states, quantitative information can be obtained on local chemical and electronic structures around sites of key atoms even in the case of complex materials. The aim of the paper is to give an insight into a recently fast-developing research field with promising practical applications, using examples for illustration such as solid-state and chemical effects on transitions in the deep atomic core, on initial- and final-state excitations, and on partial densities of electronic states obtainable from resonant Auger spectra. In addition, the role of the various electron energy loss processes, due to phenomena attributable to electron transport and to the sudden appearance of core holes, as reflected in the experimental electron spectra, will be discussed, together with suitable models for describing these processes.