Neverwinter Nights: Hordes of the Underdark is an expansion pack for the Neverwinter Nights game produced by BioWare and published by Infogrames Entertainment (now Atari).

Neverwinter Nights is a third-person perspective computer role-playing game that uses the Third Edition of the Dungeons & Dragons rules, with minor revisions. This expansion scenario pack added new features to the core game engine and a complete game scenario. The new game features include:

• 6 additional prestige classes
• 16 new creatures
• 50 new feats
• 40 new spells, divided more or less evenly between arcane and divine.
• 4 new tilesets
• additional scripting abilities for those who use the Aurora toolkit.