Macintosh File System (MFS) was the first file system used by Macintosh computers. It was a flat file system (all files were stored by the system on the root level of volumes), but had a mechanism that allowed users to create the appearance of folders in the Finder by renaming the always-present folder "Empty Folder," which would then be re-created. Folders within folders were not supported.

MFS internally supported file names up to 255 characters, but the Finder only supported 63 characters and System 7 only supported 31 characters on MFS volumes.

MFS supported resource forks for attaching data and metadata to a file.

MFS was the native file system for System 1 and 2. It was replaced by Hierarchical File System (HFS) in System 3, and was supported through Mac OS 8.1.