title_body: eBook format in nowadays: EPUB is de facto standard?
upvoted_answer: First, a note: I will not be considering PDFs in this answer, because I do not consider PDFs to be ebooks. There are a number of reasons for this, like lack of reflowability and end-user customization options, but the primary reason is that PDFs are not generally sold at sites that sell ebooks--you can't sell your PDFs through iBooks or the Kindle store or whatnot. Others have other opinions, and that's fine&mdash;the relevant info is that I won't be considering PDFs here.
  
  In terms of variety of devices supporting the format, epub is the clear standard&mdash;it's supported on nearly everything that reads ebooks. When you look at numbers, though, it's a different story: according to an article at Digital Book World, a recent Book Industry Study Group found the following statistics to the question "Where do you typically acquire ebooks?":
  
  Amazon.com website: 51.3%
  Amazon App: 15.7%
  iBooks/iTunes (Apple): 8.2%
  Barnes &amp; Noble App: 6.1%
  Barnes &amp; Noble website: 5.7%
  All other sources: 12.8%
  
  
  This means that Amazon accounts for roughly 2/3 of the sales of ebooks, making their proprietary mobi/KF8 format the dominant format.
  
  In essence, there is no "winner" yet, and there is not likely to be any time soon. Apple, Google, Barnes &amp; Noble, and Kobo are enough to ensure that epub will remain alive and kicking for quite some time. With a majority of the sales, Amazon has no impetus to switch to a standard, and they don't appear to be in any danger of losing much market share. Where we are is where we're likely to be for quite a while, which means making two formats: epub and mobi/KF8. fortunately, Amazon has gotten much better at making tools that convert from epub to their format, so concentrating on epub will give you something for Amazon as well with little extra work.