Today, the publishing business is in turmoil. For 500 years, the methods and practices of book publishing remained largely unchanged, but today the industry finds itself faced with the greatest challenges since Gutenberg.

These challenges are the outcome of two processes. On the one hand, the publishing business has been transformed beyond recognition by a set of profound social and economic changes that have been underway since the 1960s, resulting in the publishing landscape we see around us today: a handful of large corporate publishers based in New York and London and owned by large multimedia conglomerates; an array of powerful agents who have become the unavoidable gateway into publishing for writers and would-be writers; and a retail landscape dominated by a dwindling number of retail chains, mass merchandisers and Amazon. On the other hand, the technological upheaval associated with the digital revolution is now having a major impact on the book publishing business. After a decade of numerous false dawns, e-books have now arrived and they are here to stay. In 2006, e-book sales amounted to only around 0.1 percent of the overall revenue of large US trade publishers - an accounting irrelevance. Today this figure is around 20 percent, and for some kinds of books, like romance, science fiction and thrillers, the percentage can be 60 percent or more - a huge change in five years. The digital revolution is disrupting many of the traditional practices of the publishing industry, opening up new opportunities and at the same time threatening to dislodge some of the players who have shaped the business of book publishing for half a century or more.

So where is book publishing now headed? Will the traditional print-on-paper book become a relic of a bygone age, a collector's item to be found only in second-hand bookstores and garage sales, much like the old vinyl LP? Will publishers - and perhaps agents too - be displaced by a flourishing of self-publishing and by powerful online retailers like Amazon who can offer to publish writers' work on royalty terms that are much more favorable than those traditionally offered by publishing houses?

The truth is, no one knows the answers to these and similar questions. Many people have opinions but no one knows a thing. There is a great deal of apocalyptic speculation about the future of publishing but most of it is just that - speculation. I've studied the publishing industry closely for the last 10 years and I've seen how often the predictions of so-called experts - often expressed with a great air of authority - have turned out to be wrong. We are living through a revolution of sorts, and one of the few things you can say for certain about a revolution is that when you're in the middle of one, you have no idea where and when it will end.

However, as I say in the new paperback edition of my book Merchants of Culture [Plume, $17.00], some short-term trends are easy enough to see. Here are seven:

First, Amazon will continue to grow as a retail channel, while bricks-and-mortar booksellers (including the bookselling chains like Barnes and Noble) will find themselves squeezed further and further, leading to more bookstore closures and downsizing on the part of the chains. In many ways, the bankruptcy of Borders in 2011 marked the end of an era, in the sense that the age dominated by the big retail chains, rolling out their superstores across America, is now over. We're entering a new era when those retail chains that remain are in a much weaker position and where Amazon has become the main retail force to be reckoned with.

Second, publishers with weak balance sheets and companies that are highly leveraged will face growing financial difficulties, the pressures on medium-sized publishers will intensify and some of the large conglomerates will probably decide that the time has come to divest themselves of their trade publishing interests, which were always a very small part of their overall business anyway, leading to further consolidation in the hands of a small number of large corporations that remain committed to trade publishing and continue to see it as a worthwhile part of their portfolio.

Third, the decline of retail space in bookstores - the shop windows, front-of-store display tables and rows of bookshelves - and the decline of book review space in traditional print media like The New York Times will make it harder for publishers to get their books noticed, so the struggle for visibility will both intensify and become displaced, as publishers are forced to devote more and more of their marketing effort to the online environment, where they will hope to find new ways of bringing their books to the attention of readers.

Fourth, the shift from print to digital will continue, though the speed and extent of the shift will vary from one type of book to another and one author to another, and income from e-books and other forms of electronic sale will become an increasingly significant part of publishers' revenues, though exactly how significant is, at this point in time, unknown - maybe 20 percent, maybe 30, maybe 50, maybe more, no one knows.

Fifth, as more sales shift to digital and the sales of physical books decline, the large publishing houses will face growing downward pressure on their revenues, calling into question their ability to generate year-on-year growth and refocusing their attention more and more on the reduction of costs and overheads in an attempt to maintain or improve their profitability.

Sixth, the infrastructure supporting the traditional book supply chain - warehouses, sales forces, etc. - will come under increasing pressure, forcing publishers to scale back their operations and look for new ways to keep the physical supply chain going while at the same time trying to shift their organizations to a new way of doing business.

Seventh, small publishing operations and innovative start-ups will proliferate, as the costs and complexities associated with the book supply chain diminish, and threats of disintermediation will abound, as both traditional and new players avail themselves of new technologies and the opportunities opened up by them to try to eat the lunch of their erstwhile collaborators.

Beyond these short-term trends the picture is much less clear. In all likelihood the future of publishing will be a mixed economy of print and digital rather than a one-way shift from print to digital, and the most successful publishers will be those who are able to structure their businesses in a way that enables them to take full advantage of both.