This chapter summarizes the basic physiology of porcine female reproduction, including: ovarian structure and function, ovarian follicle development (folliculogenesis), the role of the corpus luteum in the establishment and maintenance of pregnancy, biosynthesis of steroid hormones (steroidogenesis) and the role of the hypothalamic-pituitary-gonadal (HPG) axis in regulating reproduction. It also describes stages of the porcine estrous cycle as well as puberty and gilt development. The chapter goes on to discuss a range of environmental factors which can impair reproductive performance, including the effects of pesticide residues and mycotoxins. Finally, the chapter reviews research on the way heat stress can affect porcine female reproductive function.