The resonant scattering of electrons by atomic systems and its interrelationship with the phenomenon of autoionization is reviewed both theoretically and experimentally. The Siegert definition of a resonance has been used to illustrate the connection underlying the various theoretical models. Particular attention has been given to the close-coupling approximation and the related effective-range theories, as well as to the formalism of Feshbach projection operators and Fano's theory of configuration interaction.