Adequate amniotic fluid volume is necessary for proper fetal growth and development. However, abnormalities of amniotic fluid volume are frequently associated with fetal disease, maternal disease, or both. Thus, an understanding of amniotic fluid dynamics and the efficacy and limitations of the various methods of estimating amniotic fluid volume can improve management and perinatal outcomes. Compared with the era in obstetric practice before the advent of ultrasonography, much is presently known about the normative values for amniotic fluid volume and the mechanisms by which this important fluid is regulated. Future research should focus on achieving a better understanding of these issues so fundamentally related to the maintenance of maternal-fetal homeostasis.