Mrs. Frisby and the Rats of NIMH

Mrs. Frisby and the Rats of NIMH is a novel by Robert C. O’Brien (pseudonym of Robert Conly), published by Atheneum in April 1971. The story revolves around that of a widowed mouse named Mrs. Frisby and her interactions with highly intelligent rats who escaped from experiments by the National Institute of Mental Health (NIMH). The book involves the themes of friendship and courage, and also alludes to the immorality of experimentation done on non-human animals.

Two sequels, Racso and the Rats of NIMH and R.T, Margaret, and the Rats of NIMH were written by O'Brien's daughter Jane Leslie Conly.

The novel was filmed as an animated feature, The Secret of NIMH, by Don Bluth in July 1982. Mrs. Frisby was renamed Mrs. Brisby because of a threatened lawsuit for copyright and trademark violation by the Wham-O company, manufacturers of the Frisbee toy. The movie was criticized for this and other plot changes, especially the change of "the secret" from a science-fictional cause to magic and wizardry.