Microinsemination, also referred to as intracytoplasmic sperm injection (ICSI), is a technique used to fertilize oocytes by delivering spermatozoa into ooplasm using micromanipulation devices. Microinsemination dose not need some of the sperm-specific properties, such as motility, acrosome reaction, or sperm-oocyte membrane fusion. So we can obtain normal offspring not only with spermatozoa but also with male germ cells that are unable to fertilize oocytes under conventional in vivo and in vitro conditions. ICSI has been widely used as an assisted reproduction technique to study the mechanisms of mammalian fertilization and to rescue male-factor infertility in humans and animals. This review describes how to apply ICSI referring to many studies and discusses future applications.