Circadian rhythms pervade all aspects of mammalian physiology, with everything from cellular metabolism through to endocrine and autonomic circuits oscillating predictably across 24 hours. The suprachiasmatic nucleus within the hypothalamus is responsible for the establishment and maintenance of circadian rhythms. Time of day information is encoded by the SCN, and then transmitted to the rest of the organism through a series of humoral and neural outputs signals. At the cellular level, circadian rhythms are generated through a transcription-post-translation feedback loop involving clock gene transcription factors. These clock genes then drive rhythmic expression of other transcription factors and functional proteins. Consequently, between 10 and 20% of the transcriptome in any given tissue is rhythmically expressed. This includes key reproductive tissues such as the ovary, oviduct and uterus, where processes instrumental to reproductive success are time of day dependent. The suprachiasmatic nucleus also signals to the medial preoptic area, tightly regulating the processes that drive ovulation. Consequently, circadian disruption can lead to a range of poor reproductive outcomes. This is most evident in the Bmal1 null mouse, which due to the deletion of a single key clock gene, display complete male and female infertility. In this presentation I will discuss recent evidence demonstrating a relationship between circadian rhythms and a broad spectrum of reproductive processes including ovulation, movement of the follicle down the reproductive tract, implantation, placentation, fetal growth and parturition. While the majority of work in this area has been conducted in rodents, I will also discuss the relevance to human reproduction, and how disrupting circadian rhythms, as occurs during shift work and jet lag, may affect reproductive capacity.