E-book sales accounted for 23% of unit sales in the first six months of 2014, according to Nielsen Books & Consumer’s latest survey of the nation’s book-buying behavior. Paperback remained the most popular format in the first half of the year, with a 42% share of unit sales. Hardcover’s share of units was just ahead of e-books, accounting for 25% of unit purchases.

Within the trade book category, adult fiction and the young adult categories both saw e-books take a 30% share of unit sales in the first half of 2014. E-books have been a significant part of adult fiction sales since the format first gained traction, but became a bigger part of the young adult category in 2012 with the success of the Hunger Games trilogy and related films. In 2014, the format has benefited from strong e-book sales in the Divergent series as well as John Green’s The Fault in Our Stars. E-book sales represented only 22% of unit sales in the adult nonfiction category in the six-month period and 13% of children’s sales, excluding young adult.

The Nielsen data also found that e-commerce outlets remained the largest sales channel in the January-to-June period. E-tailers, led of course by Amazon, had a 39% share of units, easily putting them ahead of bookstore chains, which had a 21% share. Mass merchandisers combined to account for 8% of units, as did book clubs and fairs. Independent bookstores had a 3% unit share in the period, according to the Nielsen survey. Among some of the major book categories, e-tailers’ share varied from a low of 25% of units in the children’s category to a high of 47% in the romance category. The high market share of romance sales through e-commerce sites no doubt reflects the higher percentage of romance titles that are bought as e-books. YA was the bestselling category at chains, while mysteries and adult nonfiction were tops at independent bookstores.

In the first half of 2014, 12% of book buyers said that they learned about the titles they purchased through in-store displays, pointing to the important role that bookstores play in discovery. The second most widely reported discovery method was similarly low-tech: 10% of consumers said that they heard about the books they purchased from friends and relatives. And 8% of the book buyers surveyed said that they discovered the titles they purchased by browsing the websites of online retailers.

This edition of the Nielsen Books & Consumer survey focuses on sales of new books (both frontlist and backlist), but, unlike past surveys, it excludes used book sales—a switch that makes it difficult to provide trending with prior years.