THEY have become the commuters' weapon of choice when staving off boredom and have threatened to forever change the way people read books.
But now the seemingly unassailable rise of e-books appears to have stalled with sales of digital novels declining for the first time since they appeared on the market.
Although still worth millions, the share of the market owned by e-books fell in the UK last month compared to figures from 2013, giving rise to a belief that the printed word may be making a comeback
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In the UK, 3.3 million e-books were sold in April 2013, according to Nielsen research, down 0.1% on the same month the previous year, while e-book sales were worth $800 million in the US during the first few months of the year, down 5%.
The figures represent the first year-on-year decline since e-books appeared, while last month hardback book sales in the UK rose by more than 10%,
The figures prompted Tim Waterstone, the founder of the Waterstones bookshop chain, to predict that the "e-book revolution" is over and that readers are returning to print to get their fix of their favourite authors.
"E-books have developed a share of the market, of course they have," he said. "But every indication - certainly from America - shows the share is already in decline. The indications are that it will do exactly the same in the UK.
"I think you read and hear more garbage about the strength of the e-book revolution than anything else I've known."
He set up the bookshop chain in 1982 and sold it in 1993. It is now owned by Russian billionaire Alexander Mamut.
Waterstone added: "The [physical] product is so strong, the interest in reading is so deeply rooted in the culture and human soul of this country that it is immovable. The traditional, physical book is hanging on. I'm absolutely sure we will be here in 40 years' time."
But experts in Scotland say that the fall in e-book sales should come as no surprise as they have enjoyed surging growth for years and have now reached saturation point.
Campbell Brown, managing director of Edinburgh-based Black and White Publishing, said: "Sales of e-books were always going to level off at some point, and that's what we're seeing now.
"Some genres of e-books are more popular than others, such as romantic fiction.
"These sorts of books appeal to readers who read a lot of the same type of book and it is just simpler to collect them on e-book.
"E-books account for between 20-25% of our sales so they are an important part of our business, and will remain so for the foreseeable future."
Printed books remain an attractive and "sensuous" product, said bookseller Laura Mustain, who runs Byre Books in Wigtown, Scotland's official "Book Town".
She said: "We sell second-hand books and we've not really been affected by the rise in e-books. People still want the physical product.
"Older books also tend to be more attractively bound and they are things that people want on their shelves.
"And then there is the simple sensuous, tactile pleasure that comes with handling a book."
One major advantage of e-books is that they cut down on the number of novels making it on to people's bookshelves.
And they also disguise what someone is reading, said Adrian Turpin, director of the Wigtown Book Festival, meaning that no-one knows if he is reading a trashy thriller or delving into a classic.
He said: "I tend to read more trashier books on my e-book because it saves on shelf space, and a lot of people are the same.
"The idea that e-books and print are mutually exclusive is misleading as most people will read both. Readers are readers at the end of the day."