In mathematics, an algebraic geometric code (AG-code), otherwise known as a Goppa code, is a general type of linear code constructed by using an algebraic curve ${\displaystyle X}$ over a finite field ${\displaystyle \mathbb {F} _{q}}$. Such codes were introduced by Valerii Denisovich Goppa. In particular cases, they can have interesting extremal properties, making them useful for a variety of error detection and correction problems.

They should not be confused with binary Goppa codes that are used, for instance, in the McEliece cryptosystem.