A file with a MOBI extention names stands for mobile pocket ebooks. They're used for storing digital books and are designed specifically for mobile devices with low band. MOBI files support things like bookmarking JavaScript frames and adding notes and corrections. How to Open a MOBI File Some notable free programs that can open MOBI files include Calibre s Stanza Desktop s Sumatra PDF s Mobi File Reader FBReader s Okular s and Mobipocket Reader . MOBI files can also be read by popular eBook readers like the Amazon Kindle and many smartphones s that support the format. Additionally many eBook readersagain like the popular Kindle devicealso have desktop software mobile apps s and browser tools that allow the reading of MOBI files. The Amazon Kindle App s is one example that supports Windows macOS and mobile devices; and Kindle Cloud Reader s can be used to read MOBI files online. Since opening eBook files like MOBI files is so popular on Kindle devices we rmend reading Amazon's instructions on sending MOBI files to your Kindle s if that's what you plan on doing with your MOBI file. You can do so from yourputer an Android device or over email s .