Washington —- “It’s like getting a present,” Christa Cothrel of Arlington, Va., says a little gleefully. The self-described bibliophile has been getting books in the mail for four years —- free.

Joan Wendland of Sterling, Va., hasn’t bought a book in 18 months, yet her bookshelves are full. She has sci-fi and fantasy, mysteries, nonfiction, audio books and one incredible Jasper Fforde novel autographed by the author. “He doesn’t come through the States often,” Wendland said.

Wendland didn’t pay a penny for any of these books. She and Cothrel are two of the thousands of people using the Web site PaperBackSwap to trade books. The autographed Fforde cost her one “credit,” which Wendland received when she mailed an old book to someone else.

Richard Pickering and Robert Swarthout founded PaperBackSwap in 2004, when Pickering was traveling for work. “I would buy paperback books at every airport that I went to. … I amassed a very large collection of read-once paperbacks,” he said. After trying to sell them to a used bookstore (“the woman went through five boxes of books and picked out four that she liked”) and failing to unload them online, he hit on the idea of a Web site where readers could trade titles for the cost of postage.

Cothrel started by listing some history books she’d used in college. “I was amazed at how many people wanted to hear about early Colonial Puritans. Within a day, [the books] were all asked for.” She uses her credits to trade for contemporary fiction and fitness books for a class she teaches. “I don’t know how many books you can write about abs, but apparently quite a few —- and think, I have all of them,” she said with a laugh.

There can be a social aspect to book swapping, too: PaperBackSwap’s organizers try to foster community through online forums. And when Wendland noticed she was mailing a book to someone locally, “I called her and said, ‘Instead of me paying postage, why don’t I meet you for lunch?’ ” The two now save books for each other and trade them in person.

BOOK SWAP SITES

> www.bookcrossing.com

> www.bookins.com

> www.bookmooch.com

> www.novelaction.com

> www.paperbackswap.com