A comparison is made between the competing processes of x-ray scattering and photoelectric absorption. The latter topic is then developed more fully, particular attention being paid to absorption fine-structure and its relevance to the study of the unoccupied energy levels available to electrons in solids. Electron wave scattering theories of metal fine-structure are outlined, together with the simultaneous plasmon emission concept for transition metals and the bound ejected electron theory for the solid halides of potassium.