It's an advanced form of in vitro fertilization (IVF) technique used in cases of severe male infertility or when other methods of fertilization have failed during standard IVF. Here's a breakdown of the process:

1. Procedure: During ICSI, a single sperm is injected directly into the cytoplasm of a mature egg using a fine glass needle called a micropipette. This bypasses many of the barriers that may prevent fertilization in cases of male infertility.
2. Preparation: Before the procedure, both the male partner and female partner undergo certain tests and evaluations to assess their fertility status. The female partner typically undergoes ovarian stimulation to produce multiple eggs for retrieval.
3. Sperm Retrieval: Sperm for ICSI can be obtained through various methods, including ejaculated sperm, surgical extraction (such as testicular sperm extraction or epididymal sperm aspiration), or sperm retrieved from a previous semen sample that was frozen.
4. Egg Retrieval: Once the eggs have matured, they are retrieved from the woman's ovaries using a minor surgical procedure called transvaginal ultrasound aspiration.
5. ICSI Procedure: Under a microscope, the embryologist selects a single sperm and immobilizes it using a micromanipulation technique. Then, using the micropipette, the embryologist injects the selected sperm directly into the egg.
6. Culture and Transfer: After fertilization, the fertilized eggs (embryos) are cultured in a laboratory for several days to allow them to develop. Typically, one or more of the resulting embryos are transferred into the woman's uterus through the cervix using a thin catheter.
7. Pregnancy Testing: About two weeks after the embryo transfer, a pregnancy test is performed to determine if the procedure was successful.

ICSI has significantly improved the chances of fertilization and pregnancy in couples with severe male factor infertility. It's also used in cases where previous attempts at IVF have failed due to poor fertilization rates.

However, it's important to note that ICSI does not guarantee success, and success rates can vary depending on various factors such as the quality of the eggs and sperm, the woman's age, and the expertise of the medical team.