In the book series A Song of Ice and Fire, A Dance of Dragons is Book 5. The HBO series just started with book 1, and this 5th book took six years to finish. It will be published in both the USA and UK on 12 July 2011. The plan is to release the ebook and print editions simultaneously.
Blame it on the 180 books mistakenly shipped in advance by Amazon, but there are advance spoilers and tidbits in the Book “a dance of dragons”, by author George RR Martin.