Although diagnostic ultrasonography (US) was developing in the late 1940s and early 1950s, it was not until the 1960s, with the availability of commercial equipment, that its usefulness in obstetrics began to be realized fully by radiologists and obstetricians around the world. Advances from A-mode to bistable and then to gray-scale static imaging were followed by the introduction of automated compound imaging and real-time US. Also, the development and initial use of Doppler US for the detection of fetal heart motion and the eventual use of pulsed and color Doppler US for the evaluation of such fetal structures as the major vessels and heart chambers contributed to increasing the usefulness of US in obstetrics. The development of specialized transducers--in particular, endovaginal probes--resulted in images of the early fetus. At the present time, the development of multiplanar, three-dimensional imaging shows great promise for more complete imaging of the fetus. The importance of US in the examination of the pregnant patient and, in particular, of the fetus has led to its worldwide dominance as the imaging modality of choice. The contributions of obstetric US to improving maternal well-being and fetal health have been recognized as a key component in all countries around the world.