Anyone's who read the books upon which HBO's Game Of Thrones is based will know that they're dense books.
We're talking upwards of 1,000 pages (A Dance With Dragons, the last published book, had 1,040 pages) and they're just jam-packed with more context, more dialogue, more of everything than the series is able to cover. In fact, they've deviated at certain points from the television series and fleshed out certain characters more than what's been done in the series.
The next in the series, The Winds Of Winter, was essentially what happened in Season 6 and has been eagerly awaited by fans since A Dance With Dragons was published in 2011. It's been seven years, and according to the latest blogpost by Martin himself, it's going to be eight years.
According to Martin himself, he's currently working on a family history novel on the Targarayens, called Fire & Blood, that will be released in two volumes. Volume One will be "completed soon," with Volume Two "hardly begun." This, in turn, means that The Winds Of Winter will likely not hit bookshelves until 2019 - at the very least.
Martin's been pretty open about the fact that the book will be published when it's published, and fans of the series know that he writes a slow pace - but that it ultimately pays off. What does mean for the TV series then? Well, not a lot. The final season will, according to HBO chief Casey Bloys, hit some time around 2019 so it doesn't really make much odds for how long it takes Martin to finish The Winds Of Winter.
In the meantime, sit tight and wait.