Extension could refer to either:
- Library extension, an optional source code module that authors may choose to compile with their own code in order to add new functionality that isn't available in the authoring system's default library.
- Category:Extensions is the IFWiki category for articles about library extensions.
- List of file extensions, the endings of file names (separated from the base file name by a period) such as .acd, .bat, .dat, .gam, .exe, .taf, .t3, .z5, .zblorb, and many more.
- Note: This is a disambiguation page.