Pelvic ultrasonography is now a must in the selection and preparation of patients for in vitro fertilization (IVF). The assessment of ovarian reserve (OR) is based on a series of clinical, biological, and ultrasound criteria. The ultrasound parameters used for this evaluation are antral follicle count (AFC), the ovarian volume, and the ovarian blood flow by Doppler measurement. Ultrasound is also useful to predict the risk of ovarian hyperstimulation syndrome (OHSS). Identifying women at risk allows the protocols to be adapted and surveillance to be increased in order to reduce the morbidity and even the mortality due to this event. Ultrasound techniques were tested to study endometrial receptivity. The measurement of endometrial thickness and echogenicity has little predictive value. Ultrasound is highly sensitive in detecting those lesions that are responsible for infertility through interference with egg migration and implantation and/or with sperm progression, such as fibroids, polyps, synechiae, or malformations.