Progesterone is essential for the transformation of an oestrogen-primed endometrium in preparation for implantation. With the advent of cDNA array technology, several researchers have applied this methodology to identify the various classes of genes that are upregulated during the window of implantation, both in animal models and human endometrium. The relative paracrine signalling of the individual prostanoids acting via their receptors to facilitate reproductive processes, such as implantation, has been largely unexplored. During adhesion of the implanting blastocyst to the endometrium, locally regulated uterine apoptosis is necessary to promote tissue remodelling and invasion of the epithelium. This process of programmed cell death is seen in rodents, where a progressive, continuous wave of induction of apoptosis is observed in the maternal tissues surrounding the conceptus in the rat. Over the past few years a great deal of progress has been made towards identifying the endocrine and local factors involved in implantation.