The zona pellucida (Latin meaning "transparent zone") is the specialized area surrounding mammalian oocytes (eggs).

[1] The zona pellucida is a translucent matrix of cross-linked glycoprotein filaments that surrounds the mammalian oocyte and is 6.5–20 μm thick depending on the species.

Its formation, which depends on a conserved zona pellucida-like (ZP) module that mediates the polymerization of egg coat components,[2] is critical to successful fertilization.

[4] The thick membrane of the zona pellucida functions to only allow species-specific fertilization; to prevent polyspermy, and enable the acrosome reaction for the successful adhesion and penetration by the sperm cell.

Successful fertilization depends on the ability of sperm to penetrate the extracellular matrix of the zona pellucida that surrounds the egg.

[citation needed] The zona pellucida is commonly used to control wildlife population problems by immunocontraception.