Apoptosis Protease-Activating Factor 1, APAF1, was originally isolated four years ago and shown to be the mammalian homologue of the C. elegans pro-apoptotic ced4 gene. Since then, the expression of APAF1 has been demonstrated to be involved in several cell death pathways, including the induction of apoptosis by the p53 tumour suppressor protein and neuronal apoptosis. In this review we will focus on the regulation of APAF1 expression, in particular with regard to recent developments in our understanding of the role of APAF1 in both tumourigenesis and mammalian development.