While resonance effects in atomic and molecular scattering processes have been known to exist for more than 50 years, the study of resonances in electron scattering and photoabsorption has rapidly developed during the past 15 years. Three reasons for this are that toward the end of the 1950s, experimental techniques became sufficiently sensitive to detect the structure of resonances, theoretical understanding became sufficiently detailed to accurately predict resonance positions and shapes, and computer power became sufficient to be able to handle large-scale calculations.