A high prevalence of maternal vitamin D inadequacy during pregnancy and at delivery has been demonstrated in various ethnic populations living at different latitudes. Because placental transfer of 25(OH)D is the major source of vitamin D to the developing human fetus, there is growing concern about adverse health impacts that hypovitaminosis D during pregnancy may have on the mother as well as the offspring in utero, in infancy, and later in life. While there is lack of consensus regarding the optimal circulating 25(OH)D concentration in pregnancy, it is evident that prior levels used to establish intake recommendations and vitamin D content of prenatal vitamin supplements were too conservative. This review summarizes vitamin D metabolism in the perinatal period, examines evidence regarding outcomes of insufficiency in the mother and offspring, discusses risk factors and prevalence of insufficiency, and considers strategies for public health intervention.