MOBI is an ebook file format created by the French company Mobipocket SA, founded in 2000, for reading books on mobile devices and e-readers. Amazon acquired Mobipocket in 2005, and the format became a foundation for early Kindle ebooks.
A MOBI file is built on the Palm Database (PDB) container and stores XHTML-based content, supporting compression, bookmarks, and optional DRM. It is closely related to the .prc format and to Amazon's later AZW formats. Amazon retired MOBI for new Kindle publishing in 2022 in favor of EPUB-based ingestion.
How MOBI Works
MOBI is the ebook format closely associated with the early Amazon Kindle, originally created by Mobipocket. Technically it stores its content inside a Palm Database (PDB) file, a record-based container originally designed for Palm OS handhelds, a reminder of just how far back the format goes. The book's text is XHTML-based (like a web page) and can be compressed with a PalmDOC-style scheme, with images and metadata held in the same database structure.
Like EPUB, MOBI produces a reflowable ebook: the text adapts to screen and font size rather than being fixed in place, which is what made it suitable for e-readers. When Amazon acquired Mobipocket, MOBI became the basis of the Kindle's early ebook formats, and for years a .mobi file was the way to get a book onto a Kindle. Amazon then layered its own formats (AZW, and later the more advanced KF8/AZW3 and KFX) on top of the MOBI foundation.
That history is why MOBI feels both familiar and dated. It was a capable reflowable format for its time, but it predates modern ebook features and is built on the aging Palm database structure. As ebooks evolved, MOBI's technical limitations (weaker support for advanced styling and layout than modern formats) became apparent.
Why MOBI Is Being Retired
The decisive change came from Amazon itself: in 2022 Amazon stopped supporting MOBI for sending personal documents to Kindle, moving to EPUB and its own modern formats instead. Because MOBI's main reason to exist was the Kindle, this effectively ended its everyday relevance. The format is now legacy, you still encounter .mobi files in older ebook collections, but it is no longer the way to put books on a current Kindle.
The practical consequence is simple: if you have MOBI files or want a book to work on modern readers, convert to EPUB, the open standard supported across virtually all e-readers including current Kindles. EPUB is the modern equivalent of what MOBI used to be, with better support and active development, so it is the natural destination for old MOBI ebooks.
When You Encounter MOBI
You meet MOBI almost entirely in older ebook libraries: books bought or downloaded in the earlier Kindle era, or files from sites that offered MOBI alongside EPUB. There is no reason to choose MOBI for a new ebook today. For any MOBI file you want to keep reading, converting it to EPUB ensures it works on modern devices and apps, since the format that gave MOBI its purpose, the early Kindle, has moved on.
Limitations
MOBI's limitations are those of an aging, retired format. It offers weaker support for modern styling and layout than EPUB, it is built on the dated Palm database structure, and, most importantly, it is no longer supported by Amazon for sending to Kindle, removing its core use case. Older MOBI files still open in some apps, but the format has no future. Converting to EPUB is the clear path for any MOBI content worth keeping.
