Sidney Dillon Ripley II (September 20, 1913 – March 12, 2001) was an American ornithologist and wildlife conservationist. He served as Secretary of the Smithsonian Institution for 20 years, from 1964 to 1984, leading the Institution through its period of greatest growth and expansion. For his leadership at the Smithsonian, he was awarded the Presidential Medal of Freedom by Ronald Reagan in 1985.
"Dillon Ripley, the Secretary of the Smithsonian Institute, a scholar who knows the world's more esoteric birds perhaps as well as anyone, and Fenwick Lansdowne, one of our finest bird portraitists, have combined their talents to produce a work which will be coveted not only by serious ornithologists but also by every collector of fine natural history books." —Roger Tory Peterson
"The Rails of the World fills up a very important gap, and it does it unusually well. The text and the illustrations are both of the highest quality, and it is also easy to read and to consult. The rails, of course, constitute one of the most interesting, attractive and widely distributed group of birds." —Jean Delacour