Supporters say they to help students understand the works, detractors say they help students avoid having to actually read them.
The company was started by a Nebraska native named Cliff Hillegass in 1958. He was working in a bookstore when he met the owner of a series of Canadian study guides called Cole's Notes, who suggested that Hillegass create an American version. Hillegass started with booklets covering 16 William Shakespeare titles; CliffsNotes now exist on thousands of works.
John Wiley & Sons, a publisher of scientific and technical publications, bought CliffsNotes in 2001.