Scribd is adding three categories to its e-book subscription service: sheet music; science, technical and medical titles; and Sesame Street titles.

Through an agreement with music publisher Hal Leonard, Scribd will add more than 2,600 selections of sheet music. The service will also now offer more than 20,000 science and technical titles from Elsevier and, beginning in the first quarter of the year, about 10 branded Sesame Street titles.

Scribd CEO Trip Adler emphasized that the new categories are being added without raising the Scribd subscription fee of $8.99/month. He noted that sheet music is one of the most searched-for categories on Scribd and that, by adding science and Sesame Street and science titles, the company is working towards making itself the “library of the future.”

When asked about the sustainability of the e-book subscription model, in the wake of Scribd downsizing its romance category and the shuttering of Scribd's major competitor in Oyster, Adler cited Scribd's growth in revenue and reading. He said that, overall, Scribd is "growing according to plan."

Adler was also quick to note that Scribd, unlike its competitors, was launched in 2007 as a digital document service. Given its early entry into the market and its multitude of offerings, it now boasts a significant user base of 80 million. “We have an organic funnel of traffic for growth," he continued. "We don’t have to pay to attract users. And our content is unique: books, comics, documents and now sheet music.”

Addressing the downsizing of the romance category, Adler said the company is looking to other areas to possibly expand. He mentioned wanting to add “more manga” to Scribd's comics offerings, a category that industry observers have often compared to romance because of the intense reading habits of its fans.

But Adler also emphasized that Scribd is still very invested in the romance category, where the fans' reading behavior is "off the charts by an order of magnitude.” Adler explained: “We’ve adjusted the category, and the turns have slowed. We still have great selection and the category is doing quite well.”