The process of placental delivery and the subsequent involution of the uterus during the puerperium are often described as the third and fourth stages of labor. This chapter presents a brief historical review concerning third- and fourth-stage events, followed by a discussion of the physiology of placental separation and uterine involution. The diagnosis and treatment of retained placenta and membranes (secundines), uterine inversion, postpartum hemorrhage and atony, and hematomas are considered. Important cultural and historical events in world history have been directly influenced by complications of involving the third stage of labor. Active management of the third stage of labor consists of the immediate administration of oxytocin after delivery of the infant, early cord clamping, and gentle traction on the cord, combined with gentle uterine massage to prompt placental separation. Periurethral lacerations, which often bleed freely, appear in the thin tissues on either side of the clitoris or urethra.