Human survival, like all mammals’, is dependent upon successful pregnancy, the characteristics of which have been subjected to strong evolutionary pressures. This selection process for optimizing reproductive outcomes is unique in that two individuals are affected at the same time, the mother and fetus, and their respective interests may be either congruent or divergent. In this chapter, we provide an overview for considering evolutionary influences on pregnancy, general physiology of human pregnancy, and interactions of the mother and fetus that can either shape a healthy pregnancy or result in complications of pregnancy. Moreover, in considering research into mechanisms of pregnancy maintenance and parturition, we discuss the challenges and opportunities of differing reproductive strategies between species, altering selection in distinct ways, and making pregnancy in women unique amongst mammals.