Fans are celebrating World Book Day on Thursday. Here, a man browses through books at the Albertine, a French bookstore and library at the French Embassy in New York. Jewel Samad/AFP/Getty Images hide caption

itoggle caption Jewel Samad/AFP/Getty Images

MIT is one of several schools that offer classes through edX, which provides free online courses in partnership with some of the country's top universities. Joe Raedle/Getty Images hide caption

itoggle caption Joe Raedle/Getty Images