As sales of electronic books and readers skyrocket, the threat of piracy and other copyright issues loom. Publishers are test-driving different litigation strategies to fight illegal downloads. They are also arguing in court that author contracts, some decades old, give them the exclusive rights to publish e-books.

In 2007, there were 147,000 e-reader sales, compared with an estimated 18.7 million in 2011 and a projected 23 million this year, according to the Consumer Electronics Association. The Association of American Publishers’ data show that e-books’ share of the so-called trade market, which includes fiction, nonfiction, and religious books for adults and young consumers, is on the upswing. In 2010, the most recent year available, e-books made up 6.4 percent of the trade market, compared with 0.6 percent in 2008.