Ryuzo Yanagimachi (柳町 隆造, Yanagimachi Ryūzō, August 27, 1928 – September 27, 2023) was a Japanese-born, American-based scientist. He made numerous key contributions to the study of mammalian fertilization, and he was also a pioneer in the cloning field. Accordingly, he assisted in fertilization technologies such as in vitro fertilization and direct sperm injection into the egg (commonly called intracytoplasmic sperm injection or ICSI), which are widely used today in human infertility clinics throughout the world. In 1997, his laboratory at the University of Hawaiʻi at Mānoa successfully cloned mice using the Honolulu technique.