Although Let’s Go would not comment on its exact sales numbers, Mercer said the drop in 2001 was “precipitous”—in-step with market-wide trends after the Sept. 11 attacks.

But Let’s Go’s troubles began in the 1990s, when Lonely Planet guides crashed bookshelves, stealing Let’s Go’s crown as the top-selling budget brand, according to industry experts.

“For many, many years Let’s Go Europe was our number-one seller out of everything in our store,” said Pat Carrier, co-owner of the Globe Corner Bookstores. “They owned the budget traveler niche. Twenty years ago, anyone who thought of themselves as a budget traveler—even if they were 60 years old—bought a Let’s Go.”

That is no longer the case, Carrier said. Today, travelers have hundreds of titles to wade through, from guides that specialize in British wit to books that target mountain bikers.

In this sea of new choices, old brands like Let’s Go can start to look tired, said Michael Spring, publisher of Frommer’s guidebooks.

“I think they’ve got an uphill battle,” Spring said. “It’s awfully hard, it’s almost impossible, once you get a sense of being passé, of coming back. There’s a high mortality rate among travel guides, and Let’s Go may be suffering just from overexposure.”

Others in the industry have more faith in the brand.

“Let’s Go provides information for student travelers that I think nobody else provides,” said Rick Steves, whose moniker headlines a popular series of travel guides. “For that, young travelers should be thankful. If they want a better guidebook, they can research and write it themselves.”

—Staff writer Elizabeth W. Green can be reached at egreen@fas.harvard.edu.