According to extensive research by the Fondazione Nazionale Carlo Collodi and UNESCO sources in the late 1990s, the book has been translated into as many as 260 languages worldwide, making it one of the world's most translated books. Likely one of the best-selling books ever published, the actual total sales since first being published are unknown due to the many reductions and different versions. The story has been a public domain work in the U.S. since 1940. According to Viero Peroncini: "some sources report 35 million [copies sold], others 80, but it is only a way, even a rather idle one, of quantifying an unquantifiable success". According to Francelia Butler, it also remains "the most translated Italian book and, after the Bible, the most widely read".