An older e-book file format that was purchased by Amazon and evolved into the Kindle format.

MOBI was originally developed by French company Mobipocket SA.

It was purchased in 2005 by Amazon and became the basis for the early versions of the Kindle format.

Some people treat MOBI as a synonym for Kindle format, but this is inaccurate as there are versions of MOBI that predated the Kindle, and newer versions of the Kindle format that are not based on MOBI.