NYX may refer to:

• Nyx, in Greek mythology, Nyx was the primordial goddess of the night
• NYX (comics), an American comic book miniseries by Marvel Comics
• Nyx (Once Upon a Time in Wonderland), the guardian of the well in the U.S. TV series
• Nyx (Image Comics), a character of the Spawn (comics) comic book series.
• NYSE Euronext, (, ) (formerly NYSE Group, Inc.) is a for-profit corporation that operates multiple securities exchanges, most notably the New York Stock Exchange (the "Big Board"), Euronext, and NYSE Arca (formerly known as ArcaEx).
• Nyx, an experimental prototype for the Amiga computer platform's AAA chipset, designed by Commodore engineer Dave Haynie in 1992 .
• Nyx, is a Gallente Mothership in the Massively Multiplayer Online Game, EVE Online
• , A 2D-3D hybrid video game for WiiWare by Over the Top Studios.
• Nyx is the name of a character in the video game Persona 3.
• NYX (gene), is a gene encoding the protein Nyctalopin
• Nyx (moth), a moth genus
• Nyx, a character in the Queen's Blade Series.
• Nyx, a recurring antagonist of the video game Hellbender.
• Nyx, a hero in the video game Dota 2.
• Nyx, a Tenno in the free-to-play video game Warframe
• Nyx (composition), an orchestral composition by Esa-Pekka Salonen

NYX may also be:

• 3908 Nyx, is an Amor and Mars-crosser asteroid
• Nix (moon), a moon of Pluto
• NYX (cosmetics), a cosmetics brand named after the Greek goddess of the same name. Founded by Toni Ko in 1999 and headquartered in Los Angeles, California.

Nyx (; , "Night"; ) is the Greek goddess (or personification) of the night. A shadowy figure, Nyx stood at or near the beginning of creation, and mothered other personified deities such as Hypnos (Sleep) and Thanatos (Death), with Erebus (Darkness). Her appearances are sparse in surviving mythology, but reveal her as a figure of such exceptional power and beauty, that she is feared by Zeus himself.