Scribd, an e-book subscription service, has secured $22 million in financing led by Khosla Ventures and including new funds from existing investors. The new funding brings Scribd’s total financing to date to $48 million.

Scribd CEO Trip Adler said that Keith Rabois, a partner at Khosla Ventures, will join Scribd’s board as an observer.

The new round of funding caps a big year for Scribd and for the e-book subscription business model. Scribd offers unlimited subscription access to more than 500,000 e-books for $8.99/month. In the last year the service added audiobooks to its offerings as well as tens of thousands of titles from HarperCollins and Simon & Schuster and now offers content from more than 1,000 publishers.

Adler said that Scribd attracts 80 million visitors a month and traffic has grown by 31% a month since the subscription service launched in October 2013. “This new funding round will enable us to work towards achieving our goal of creating the most comprehensive library of the future for our millions of users around the world,” he said.