This chapter examines the evidence suggesting why sexual intercourse around the time of embryo transfer is beneficial to in vitro fertilization (IVF) outcomes. Three studies have examined if artificial exposure to whole semen or seminal plasma at the time of oocyte retrieval may alter IVF implantation rates. The observations that improvements in IVF pregnancy rates seen in women with tubal factor infertility undergoing artificial insemination using whole semen or sperm-free seminal plasma suggests that the mechanism for action is not simply natural conception but rather a beneficial effect on embryo development or endometrial receptivity. In the rodent model exposure of the female to semen produces an inflammatory reaction within the endometrium with the release of cytokines such as granulocyte macrophage colony-stimulating-factor (GM-CSF) that are known to have positive effects on embryo development. However, intercourse is not advocated for women experiencing pelvic discomfort related to an exaggerated hyperstimulation response.