An iMovie Library file, identified by the .imovielibrary extension, is a specialized package format used by Apple's iMovie video editing software on macOS. Rather than being a single flat file, it is a macOS 'bundle' or folder structure that acts as a central repository for all elements of a user's video projects. It contains the original source media, including raw video clips, photos, and audio files, as well as metadata, render files, cache data, and the database files that track every edit, transition, and effect applied within the application. This package-based approach allows iMovie to perform non-destructive editing, ensuring that the original footage remains untouched while the software records the instructions for how to assemble the final video. Because it consolidates all project assets into one location, users can easily move their entire workspace between different hard drives or computers. While it appears as a single icon in the macOS Finder, its contents can be viewed by right-clicking and selecting 'Show Package Contents'. These files can grow significantly in size depending on the resolution and volume of the imported media.