With rapid development of ultrasound technology, its clinical application is expanding and deepening. This book is focused on practical application of ultrasound in obstetrics and gynecology. Besides ultrasound diagnosis, the new progress of ultrasound in obstetrics and gynecology, such as interventional ultrasound, 3D ultrasound, and endoscopic ultrasonography, is also discussed. Typical images selected from abundant cases are provided with concise and refining key points. It serves as a valuable reference for sonologists, radiologists and gynaecologists for accurate diagnosis.