Metal Gear Acidメタルギア アシッド (Metaru Gia Ashiddo), stylized as METAL GEAR AC!D, is a turn-based collectible card tactical RPG video game developed by Konami Computer Entertainment Japan for the PlayStation Portable. The game was first unveiled at E3 in May 2004, and was released in Japan on December 16, 2004, in North America on March 24, 2005, and in Europe on September 1, 2005. It was a launch title for the PSP, though a Java ME version for mobile phones was released by Glu Mobile in 2008 titled Metal Gear Acid Mobile.

Acid focuses on turn-based tactics, using a trading card-based system to control the main character's movements and actions. Acid in the name stands for "Active Command Intelligence Duel". The cards are not truly collectible, as the game is complete with a single purchase. However, the game does feature deck design and deck optimization elements. The game allows for multiplayer gameplay by wireless ad-hoc connections of two PSPs.