You can view or print your catalog instantly, sorted by author, for example, or by more personal tags like “books that mention Venice,” “books that touch on digital photography” or “books I’ve loaned out.” Collections can also be displayed by book covers.

Ms. Havemann, for instance, has catalogued all of the 2,956 volumes at her home, and no longer has to rely on hand-written notes or a spreadsheet. Now, as she collects new books — an unending and delightful process — she uses a portable bar-code scanner to accumulate their ISBNs, then downloads up to 500 entries at a time onto LibraryThing.

But the swift, accurate cataloguing of her books is not what she prizes most about LibraryThing.

“I love the social aspect,” she said.