The mystery genre has retained its popularity over the years. Whether a classic “whodunit,” a cozy, a police procedural, or some new hybrid of mystery/suspense plus fantasy, sci-fi or horror, crime fiction still draws a strong audience of readers.

Surveyed for Library Journal’s annual round-up of trends in the mystery genre, more than half of the 232 librarians polled say mysteries are the most popular book genre they offer, as measured by circulation, shelf-space—accounting for almost a quarter of their print fiction materials—and e-collections, making up more than 20% of libraries’ ebooks.

While e-collections are growing (and most publishers have finally agreed to sell ebooks to libraries now), which e-mysteries they buy depends heavily on patron demand and costs. Ebook purchases are now about 6% of libraries’ acquisitions budgets, up from 1% three years ago.

“E-books aren’t the future of mystery, they’re the present,” said Soho Press publisher Bronwen Hruska. They accounted for two-thirds of the sales of the Soho Crime imprint in 2012 and half or more of sales by another mystery publisher, Minotaur. Sisters in Crime’s recent interviews with publishers revealed that while e-books are “the fastest growth sector for publishing revenues,” the effect on income—publishers’ or authors’—is not yet clear.

Amazon’s heavy promotion of low price-point books for the Kindle through various deals and free offerings has helped even a few new writers achieve electronic sales that outsell print. An example is when Leonard Rosen’s debut thriller, All Cry Chaos, was picked as a Kindle Book of the Day and sold 7,000 electronic copies and 4,000 print.

Presumably, it helps to write a good book, too. But quality—good or bad—isn’t a guarantee of sales numbers when so many books are free or $.99.