We derive an expression to describe generation and recombination processes through intermediate defect states. The expression is based on the well-known Shockley-Read-Hall formalism, but includes both radiative and non-radiative transitions. The concept of radiative recombination coefficients of impurity states is introduced and expressions to calculate them are given. The new formalism may be of use in the study of novel photovoltaic and optoelectronic devices. (C) 2002 Elsevier Science Ltd. All rights reserved.