Better yet, the official product page is here. I was told the book would be released in August, but it says June here, so who am I to argue?
It’s also available for preordering at Amazon.com. Although Amazon lists the book at 256 pages, Wizards claims that it’s 192. I’d go with Wizards on this one. Either way, I encourage you to preorder it through your local game store first if you can.