Superovulation is very important technique used to increase the number of ovulated follicles. Those follicles considered as a source of oocytes for in-vitro fertilization or fertilized to be a source of embryo transfer. It has been recommended to perform superovulation at the middle of the oestrous cycle. The idea supporting this recommendation was the emergence of the second follicular wave and well developed CL with high progesterone level. In this book we examined the effect of low progesterone level on the development of the superovulated follicles and the interaction between E2, GH, and IGF1. In the second part we compared three protocols of superovulation and their effect on the follicle growth, numbers and ovulation.We hope that the book can help the researcher to understand the superovulation variability and giving new ideas for controlling it.