“To Kill a Mockingbird” has at last joined the modern world … albeit five years after everyone else.

Harper Lee, the book’s 88-year-old author, has at last agreed to let her publisher, HarperCollins, release the classic as an ebook. (“I’m still old-fashioned,” she said in a statement. “I love dusty old books and libraries.”) It’s amazing that Lee kept “Mockingbird” off the Internet this long. But it’s even more amazing she isn’t alone — dozens of classic books aren’t available as ebooks. We counted more than a dozen from the Modern Library’s lists of top classic novels, alone. Among the stand-outs:

  1. “The Catcher in the Rye,” by J.D. Salinger
  2. “Finnegan’s Wake,” by James Joyce
  3. “The World According to Garp,” by John Irving
  4. “The Wapshot Chronicles,” by John Cheever
  5. “The Death of the Heart,” by Elizabeth Bowen
  6. “Ironweed,” by William Kennedy
  7. “The Moon is a Harsh Mistress,” by Robert Heinlein
  8. “Fifth Business,” by Robertson Davies
  9. “The Wood Wife,” by Terri Windling
  10. “At Swim-Two-Birds,” by Flann O’Brien
  11. “The Cunning Man,” by Robertson Davies

… on top of that, Gabriel Garcia Marquez’s work is only available in Spanish. And in March of last year, when Book Riot’s Jeff O’Neal tallied up the ratio of prize-winning books available as ebooks or in print, he found that “pretty consistently between 10-15% of any given list of novels still under copyright are only available in print.” Many of the notable books he mentions, including “The Time Traveler’s Wife” and “Rebecca,” have since been digitized — but only within the past six to eight months.

What, exactly, is going on here? The short answer is that the book industry, like all publishing industries, has been slow to embrace change: While ebooks now comprise 30 percent of book sales, per the Book Industry Study Group’s most recent report, they were long seen as a novelty for early adopters. After several years on the market, however, ebooks have fallen into what BISG calls “reasonably predictable consumption patterns” — they’re a known quantity. Publishers want in.

That doesn’t mean anything, however, if the book’s rights’ holders oppose digitization. That was the case of “To Kill a Mockingbird” — the famously litigious Lee held out against giving up ebook rights for years. Likewise Joan Didion’s essay collection “Slouching Toward Bethlehem,” because it first appeared in magazines and newspapers and Marquez’s English translations, which are owned by Marquez and his translators. Meanwhile, some books — like Irving’s “The World According to Garp” — are available as ebooks, just not in the U.S.

In either case, many publishers and rights’ holders have elected to go digital very recently: See Thornton Wilder’s “The Bridge of San Luis Rey” (published as an ebook Feb. 25), Jean Rhys’ “Wide Sargasso Sea” (Jan. 28), Max Beerbohm’s “Zuleika Dobson” (Jan. 14) … and now, at long last, “Mockingbird”!

That ebook comes out July 8 and will cost $9.99 on Kindle, about the twice the cost of the physical, mass paperback book. Is that a last, sly stab from Lee and co., or just the economics of the business? Who cares! We’re just glad it’s finally online.