X++

X++ is the object-oriented programming language used to develop, customize and extend Microsoft Dynamics 365 Finance & Operations (and its predecessor, Dynamics AX). It combines language features similar to C# and Java with direct, first-class access to the database and the application's data model.

Developers use X++ to build custom tables, forms, classes and data entities, and to extend standard behaviour through the extension framework and the Chain of Command pattern — adding logic without overlaying or breaking Microsoft's code, which keeps the system upgrade-safe.