Leanpub:
You can buy .epub, .mobi, .pdf versions from Leanpub. If you want a digital edition, then please buy from Leanpub. Order Now!
Amazon:

Print Edition Is Available On Amazon, too!

Kindle is also available in these Amazon territories. That said, if you want the digital edition, I hope you'll consider buying it from Leanpub first. It's better for me and the publishing industry if more people buy from them. :) US IN UK FR DE ES NL JP BR CA MX AU