Fetal surgery, as defined for the purpose of this chapter, is the act of opening the gravid uterus, surgically correcting a fetal abnormality, and returning the fetus to the uterus for postoperative recovery and continued gestational development. By this definition, human fetal surgery has now been performed for more than a decade, primarily at a single center (1). Tremendous progress has been made in our understanding of the natural history and pathophysiology of fetal disease, in solving the technical challenges of fetal surgery, and in intra- and postoperative care and monitoring of the maternal-fetal unit. However, success and general application of fetal surgery continue to be limited by a number of unsolved and formidable problems. The most important of these is the control of preterm labor, which is the Achilles heel of fetal surgery. Preterm labor is to the infantile field of fetal surgery what rejection was to the field of transplantation. The discovery of effective tocolysis would be analogous to the development of effective immunosuppression and would allow fetal surgery to achieve its full potential. In addition, less invasive methods of operating on the fetus are emerging that will further reduce the maternal and fetal risk of this currently highly invasive treatment.