The process of post-lactational regression, or involution, of the mammary gland is a complex event characterised by extensive death of the secretory epithelium coupled with remodelling of the extracellular matrix and adipogenesis to regenerate the fat pad. Associated with these events is an inflammatory cascade and acute phase response. The critical signalling pathways that regulated involution have been defined and a wide variety of genes have been shown to modulate the various processes involved, including cell death, phagocytosis, tissue remodelling and innate immune response.