 Founded in 1947, EN provides critical funding and support for educational and interpretive programs in America’s national parks and other public trusts.They began the national park passport stamp program in 1986, and as of February 1, 2006 have sold 1.3 million passport books.To commemorate the 20th anniversary of the program, they created the "Passport Explorer", a new version of the passport book with larger, sturdier pages, in early 2006.