Ultrasound is widely used in assisted reproduction, and the scan operator is responsible for “driving” the ultrasound equipment. This requires a working knowledge of the basic and technical aspects of ultrasound and the scanner settings, and an understanding of the potential thermal and mechanical bioeffects. This chapter covers the basic principles of sound, the generation of ultrasound, the interactions of ultrasound with tissue, real-time B-mode imaging, the basic principles of Doppler ultrasound, machine controls and image optimization, and the safety of ultrasound.