The immune response is centrally involved in all aspects of the reproductive process, from generation of gametes, conception and implantation, to fetal and placental development and birth. In contrast to early theories about immune suppression, immune cells and cytokines play an active role, resulting either in immune tolerance and permissive effects on development, or immune effector function which is important in sensing and selecting healthy gametes and embryos, and mediating parturition and birth. Many forms of infertility and pregnancy disorders have an immune aetiology. Australian reproductive biologists have been instrumental in defining the fundamental biology of how immune cells and cytokines can act to both facilitate or impede reproductive events and processes, and impact developmental programming and offspring health. Their work has led to new understanding of how the reproductive and immune systems work in collaboration to ensure quality control and maximise genetic diversity and fitness in outbred populations, and is now contributing to development of new clinical treatments involving targeted modulation of the immune response.