This chapter outlines the principles and techniques of prenatal diagnosis and discusses some potential future developments in prenatal diagnosis. Prenatal diagnosis of congenital birth defects or genetic disorders is based on screening a low-risk population. First-trimester sonographic assessment of fetal anatomy has become an important component of prenatal diagnosis. A number of different views of the fetus are available with 3D ultrasound, such as surface rendering to display the skin surface, transparency mode, and maximal intensity mode. The introduction of ultrafast imaging methods such as echo planar imaging and single shot fast spin echo techniques allow the acquisition of single, high-resolution images in less than one second and have made magnetic resonance imaging (MRI) examination of the fetus a real possibility. Invasive tests in pregnancy are used to obtain fetal cells, fluids, or tissues that are used for prenatal diagnosis of aneuploidy, fetal congenital disease, and fetal infection.