As a medieval historian with some decidedly old-school habits, Guy Geltner wanted to expand his online presence, but he shuddered at the thought of "friending" or "Tweeting" to get other scholars' attention.

Then a colleague introduced him to Academia.edu, one of a growing number of networking sites designed specifically for scholars.

"Friends told me that it's basically Facebook for nerds, which I'm very happy with," says Mr. Geltner, a professor of medieval history at the University of Amsterdam.

The profile he set up includes far more information than his university's Web page could accommodate, including links to research papers, books, blogs, and forthcoming talks. It lets people know what he's working on and helps him connect with others in his field. "I like the fact that I can read someone's paper without having to be their friend or follower," he says.

Still, he isn't averse to helping out a scholar in need. When a query popped up in his Academia.edu window from a doctoral student...