| Pseudonym: | Eth Clifford; Ethel Rosenberg; Ruth Bonn Penn; David Clifford |
| Birth Date: | 25 December 1915 |
| Birth Place: | New York, New York, U.S. |
| Death Place: | Pikesville, Maryland |
| Occupation: | Writer |
| Period: | 1949–1998 |
| Genre: | Children's, young adult |
| Notableworks: | Flatfoot Fox, Jo-Beth and Mary Rose Mysteries |
| Awards: | 1982 Young Hoosier Award |
| Spouse: | David Rosenberg |
| Children: | 1 daughter |
Ethel Clifford Rosenberg (December 25, 1915 – April 1, 2003) known professionally as Eth Clifford or Ruth Bonn Penn, was an American children's fiction writer, best known as the author of the Flatfoot Fox and Jo-Beth and Mary Rose Mysteries series.
Clifford was taught to read in a one-room schoolhouse, and grew up an avid reader. It was when her family moved to Philadelphia that she was able to first avail herself to the public library. At the age of sixteen, she met her future husband, David Rosenberg, at a poetry reading in Brooklyn. While Rosenberg was away, serving in World War II, he encouraged Clifford to begin writing, and she did so, publishing her first novel for adults in 1949, with a sequel of sorts, featuring the recurring character "Uncle Julius", published in 1951. That her married name was Ethel Rosenberg and her first two books prominently featured a character named Julius is a remarkable coincidence, and apparently helped drive her subsequent use of the Eth Clifford byline. Her subsequent books were written for children, and her 1979 novel Help I'm A Prisoner in the Library! earned her the prestigious 1982 Young Hoosier Award.
Together with her husband, she founded David-Stewart Publishing company. When co-authoring a book, the two would write under the portmanteau pen name of David Clifford.
Clifford died on April 1, 2003.