SummeryTwo-dimensional viewing of three-dimensional anatomy, using conventional ultrasound, limits clinicians' ability to quantify and visualize a number of diseases. It is one reason for the reported variability in ultrasound diagnosis. Two-dimensional ultrasound has several limitations. The 2-D ultrasound image represents a thin plane at an arbitrary angle in the body; it is difficult to localize the image plane, and reproduce it at a later time.SummeryOver the past two decades, investigators have developed 3-D ultrasound imaging techniques. The authors describe various approaches, including techniques for acquiring the necessary information to produce and view a 3-D image via computer. The various developments are discussed in regard to their applications and current limitations. Examples are given from developments of 3-D B-mode, color Doppler, and power Doppler systems for imaging various organs.