The company has managed to avoid supporting the epub format for more than fifteen years.
If that has been a sticking point for you, there's good news - sort of. Kindle will soon be "supporting" the epub format!
We say sort of, and use "supporting" in quotes because although it would be easy for the company to simply enable their ubiquitous readers to support epub, that's not actually what the company has planned. Instead, Amazon will issue an update to Kindles that will allow them to convert epub files to a proprietary format that can be read by their readers.
Kindle users have gotten by for the past fifteen years by using a program called Calibre, which has a somewhat convoluted routine that converts epub files into the Kindle's native file format. The results were sometimes not great, but it got the job done. Even so, it has proved to be intensely frustrating for Kindle users who have complained loudly to Amazon, but to no avail.
Now, finally, Amazon is listening - again, sort of.
Early user reactions to Amazon's announcement have not been favorable, but the company continues to show absolutely zero interest in genuinely supporting the epub format.
In some respects, it's easy to understand Amazon's position. The truth is that at this point, they're likely alienating enough people with their hardline position against the epub format that they're not doing themselves any favors.
At any rate, if you own a Kindle you'll soon be able to convert epub files to something called KF8 and view them on your device. It's not a great solution but it's an improvement over what exists today.