The Bad Seed is a novel by William March which was adapted into a play by Maxwell Anderson.

The central character of the story is Christine Penmark, a young mother who is horrified by her daughter Rhoda's misbehavior. Influenced by a landlady's dalliance in psychiatric theories and a chance visit from her father, Christine begins to recall her own childhood, which brings back memories of times before the people she remembers as her parents adopted her. She eventually figures out that she was actually the sole surviving daughter of "The Incomparable Bessie Denker," a well-known (fictional) serial killer. Bessie Denker's career is based very roughly on the real-life careers of Jane Toppan and some other "black widow" serial killers, and the description of her execution is based on that of Ruth Snyder.

Rhoda is portrayed as a sociopath, although the term was not in use at the time of the book. Like her real grandmother, she has no conscience and will kill if necessary to get whatever she wants, whether that be a penmanship medal she felt she should have won, the silence of a janitor who knows more than she wants him to, or an opal pendant. By the time Christine manages to put the truth together, Rhoda has already killed two people. She depends heavily on charm, and can easily charm adults---other children can sense something wrong with her, and fear and are repulsed by her.

Once her mother has come to the correct conclusions, she has to wrestle with a terrible dilemma. As young as Rhoda is, there are no guarantees that any arrangements made to confine her will prove permanent, and there would be a huge glare of publicity. At the same time, Christine knows full well that Rhoda will certainly kill again, and again; her grandmother is thought to have begun her career very young, by "accidentally" putting arsenic on bread she knew her brother would eat, and went on to kill over twenty people before her career ended.

The play was adapted by John Lee Mahin for the screenplay of a 1956 movie directed by Mervyn LeRoy and starring Nancy Kelly, Patty McCormack, Henry Jones, Eileen Heckart, Evelyn Varden , William Hopper, Paul Fix and Jesse White .

The movie was nominated for Academy Awards for Best Actress in a Leading Role (Nancy Kelly), Best Actress in a Supporting Role (Eileen Heckart and Patty McCormack, separately) and Best Cinematography, Black-and-White.

Although the novel and play had the mother dying and the evil child surviving, the Hays Code did not allow for "crime to pay". The ending of the film thus has it the other way around, with Christine's life being saved by the local hospital and Rhoda being struck down by lightning while trying to retrieve the penmanship medal from a lake. (As a topper, during the "curtain call" credits, Nancy Kelly (in character) hauls Patty McCormack over her lap and gives her a sound spanking for her misdeeds.)

The Bad Seed was made for television in 1985, adapted by George Eckstein and directed by Paul Wendkos . It starred Blair Brown, Lynn Redgrave, David Carradine, Carrie Wells , Richard Kiley, Chad Allen and Christa Denton .

"Bad Seed" is also the name of the Nick Cave biography by Ian Johnston.