Among iTunes’s top classical albums are plenty by Yo-Yo Ma and Glenn Gould. But the list is also filled with budget compilations, like “The 50 Most Essential Pieces of Classical Music” and “Beethoven: 100 Supreme Classical Masterpieces,” that pack in dozens of “1812” Overtures and “Für Elises” for as little as $6.

One label dominates these collections: X5 Music Group, a 10-year-old Swedish company that has built a $14 million business applying the strategies of online marketing to classical music. Its success has spawned numerous imitators and led to a new deal that allows it to exploit the classical and jazz catalogs of the Universal Music Group, the world’s largest record company.

X5 began in 2003, the year Apple opened its iTunes store. The three founders, including Johan Lagerlof, a former dance-music producer, spotted an opportunity for an online-only label and began approaching record companies to license their digital rights. Its first deals were with small classical labels in Europe, even though the founders had no experience with Brahms and Mozart.

“We were pop guys, and maybe that was good,” said Mr. Lagerlof, a soft-spoken 42-year-old, in a recent interview at the company’s New York office, on the 75th floor of the Empire State Building. “We weren’t experts. We created products that we could easily find in stores and easily understand.”