The sperm is frozen in liquid nitrogen at 196 degrees below zero. The place where you crioconservano tubes with sperm is what is called a Sperm Bank.
The seed can be either from an anonymous donor who donates to help a couple or a woman to have children, or it can come from a man who wants to save his seed for his later use due to treatment that could impair his fertility or before a vasectomy.
Law requires that donor sperm is frozen. It is not permitted to use fresh sperm from an anonymous donor.
Another reason to practice freezing of semen and if you enjoy an in vitro fertilization with donated eggs with eggs, so as to avoid any possibility of contact who gives the egg and the couple.
Or freeze the seed for the man for psychological reasons or otherwise, can not provide the sperm for fertilization.
Sperm can be cryopreserved for years, leaving intact its capacity to fertilize.