# External source files

If your project uses source files located outside the [project root](project.html#ProjectRootDirectory), CLion will add them or the corresponding directory to the [Project tree](project-tool-window.html) as present in the file system:

![External sources in the Project tree](https://resources.jetbrains.com/help/img/idea/2026.2/cl_outsideroot_tree.png)

## See also

### Reference

[Project tool window](project-tool-window.html)