According to the New York Times, romance e-books are the fastest-growing category of the e-reading market, topping fiction, mystery, and science fiction. Publishers have known for years that romance novels sell well, accounting for nine to ten percent of overall sales, but now that e-books have taken off, they’re seeing some compelling changes. This year, sales have doubled at All Romance, an online retailer that only sells e-books.

“It’s easier to check out some naughty little title online than in a brick-and-mortar store where your pastor could step up in line behind you,” said Barb Perfetti, chief financial officer of All Romance. “We’ve had lots of customers write to us and say, ‘Now I don’t always have to show my husband what I’m reading.’”

In 2009, romance fiction accrued $1.36 billion in sales, giving it the largest overall share of the trade-book market, according to Romance Writers of America, which collects data on romance books. The RWA also claims nearly 75 million people read at least one romance novel in 2008.

Barnes & Noble has begun to market romance e-books harder than ever. “This is a new business for us,” said William Lynch, chief executive. “Romance buyers are buying, on average, three books a month. That buyer is really, really valuable.”