Ultrasound scanning (USS) plays an indispensable role in the assessment, management, and treatment of subfertile couples. The current conventional practice of using transvaginal scanning during assisted reproduction treatment (ART) involves assessment of endometrial status after downregulation or at the start of a treatment cycle; assessment of follicular response to ovarian stimulation and risk of ovarian hyperstimulation syndrome (OHSS); assessment of endometrial thickness before fresh or frozen embryo transfer; and ultrasound-guided oocyte retrieval and embryo transfer. Researchers identified that USS imaging is the only constituent of ART that is not regulated by a quality assurance (QA) program. USS is perceived to be safe, and it takes 10–15 minutes to complete. However, appliance design and functions are constantly being modernized, and USS can only be considered safe if used appropriately by well-trained users who regularly maintain their skills. This chapter describes the controversies reported in the literature about the different ways to perform COS monitoring by USS and estradiol (E2); a description of the different techniques and software for the measurements of the follicles available in the literature and the reproducibility of the results. Finally an overview of simulation, training, and QA with implications for future research is given.