Katherine Kelley is an American journalist and author of best-selling unauthorized biographies of Jacqueline Kennedy Onassis, Elizabeth Taylor, Frank Sinatra, Nancy Reagan, the British royal family, the Bush family, and Oprah Winfrey.

An unauthorized biography sometimes called a kiss-and-tell, or a tell-all, is a biography written without the subject's permission or input. The term is usually restricted to biographies written within the subject's lifetime or shortly after their death; as such, it is not applied to biographies of historical figures written long after their deaths.