This chapter briefly reviews the embryology of the male reproductive system, whose knowledge is required to understand the physiopathology of cryptorchidism and of hypospadias. One distinctive feature of hormone secretion through the hypothalamus-pituitary-gonadal axis is that they regulate their own secretion through negative feedback inhibition. Androgens are essential for spermatogenesis, maturation of secondary sexual characteristics, masculine settlement of the bone-muscle apparatus, and libido. Testosterone is the most important circulating androgen in men's blood. Sperm progression in the seminal tract during ejaculation and contractions of the epididymis are supported by oxytocin and guided by sympathetic and parasympathetic nerves. Sperm-egg interaction is a specialized process that leads to fertilization. The occurrence of acrosomal exocytosis facilitates sperm penetration through the zona pellucida, and exposure of certain molecules on the sperm equatorial segment that participate in fusion with the oolemma.

In-vitro fertilization (IVF) has rapidly become a treatment for male factor infertility. Mature oocytes are inseminated in a Petri dish and examined 18 hours later for morphologic proof of fertilization. Gamete intrafallopian transfer (GIFT) is designated for women who have at least one functioning fallopian tube. Micromanipulation procedures progressed because of discouraging results with IVF for the male-factor patient. Although application of acid solutions or enzymes, and mechanical opening of the human zona pellucida have been developed, only partial zona dissection (PZD) has been successful in humans. One of the most significant risks associated with ART is the ovarian hyperstimulation syndrome (OHSS). Preimplantation genetic screening (PGS) for aneuploidies has been performed in patients with advanced maternal age, unexplained recurrent miscarriage, recurrent implantation failure, nonobstructive and obstructive azoospermia (NOA and OA), and severe sperm morphology anomalies.