Embryo transfer is the final success-determining step in an in vitro fertilization cycle and, as any other steps, depends on optimizing a number of conditions. This chapter starts with a brief overview of the history followed by a systematic description of variables that could influence the final outcome. The up-to-date evidence is scrutinized and presented. The ultrasound scan became an important part of the process. It can help not only with access to the cavity in cases of tortuosity of the cervical canal but also in depositing the embryo at the appropriate place in the uterine cavity. Where alternative access to the cavity is required, the procedure would not be possible without ultrasound guidance. It is important to ensure that robust training and quality control systems for monitoring performance are in place to ensure continuous improvement.