Nim Chimpsky (November 19, 1973 – March 10, 2000) was a chimpanzee used in a study to determine whether chimps could learn a human language, American Sign Language (ASL). The project was led by Herbert S. Terrace of Columbia University with linguistic analysis by psycholinguist Thomas Bever. Chimpsky was named as a pun on linguist Noam Chomsky, who posited that humans are "wired" to develop language.

Over the course of Project Nim, the infant chimp was shuttled between locations and a revolving group of roughly 60 caregivers, including teenagers and grad students, few of whom were proficient in sign language. Four years into the project, Nim became too difficult to manage and was returned to the Institute for Primate Studies in Oklahoma.

After reviewing the results, Terrace concluded that Nim mimicked signs from his teachers in order to get a reward. Nim learned a variety of signs through a process of reinforcement, but these signs were not a result of creative or spontaneous language use. Terrace argued that Nim did not initiate conversation or create sentences. Nim primarily learned this in order to get what he desired, such as food each time he correctly produced a sign. Terrace said that he had not noticed this throughout the duration of the study but only upon reviewing video tape. Terrace ultimately became a popularly cited critic of ape language studies. This pattern of learning, where signs were used mainly as tools to obtain rewards, suggests that Nim did not acquire the complexities of grammar or syntax, which are central elements of human language. This finding strongly supports Noam Chomsky’s theory that humans are biologically predisposed to learn language in a way that is fundamentally different from animals, who lack this innate linguistic ability.

Herbert Terrace, a professor of Psychology at Columbia University, launched Project Nim in 1973, six years after R. Allen and Beatrix Gardner began testing a chimpanzee's ability to acquire American Sign Language with Project Washoe. Terrace named the infant chimpanzee as a pun on Noam Chomsky. With this project, Terrace intended to challenge Chomsky's assertion that only humans can use language. (Terrace's mentor, B.F. Skinner, a key figure in behaviorism, was known as an academic target and rival of Chomsky.)

Nim's life history is detailed in Elizabeth Hess's seminal biography, Nim Chimpsky: The Chimp Who Would Be Human (2008), which became the basis for a 2011 documentary film directed by James Marsh, Project Nim (see below).

Nim was born at the Institute for Primate Studies in Norman, Oklahoma. A few days after his birth, he was taken from his sedated mother and placed in the New York City home of Stephanie LaFarge. LaFarge was a former grad student of Terrace's with three children and four stepchildren. LaFarge "knew nothing" about chimps and instantly recognized that the arrangement would be a problem. The LaFarge household was unconventional: she breastfed the chimp (though she had no milk) and smoked pot with him. Stephanie LaFarge and her daughter Jennie Lee used signs sporadically, focusing instead on play and establishing trust, which they saw as a developmental need. They did not maintain records of Nim's development and did not support the harsh discipline practices that Terrace and his lead trainer at the time demanded. (This included the use of cattle prods and forcing Nim into a small, dark box when he misbehaved.). By mutual agreement two years later, Nim was moved out of the LaFarge brownstone and into a large house in Riverdale, where a grad student, Laura-Ann Petitto, took over as primary caregiver.

After the move to Riverdale, Nim exhibited symptoms of intense anxiety. For the first few weeks, he refused to be alone for even a minute. When left with a new person, he would rip off his clothes and urinate and defecate all over the room. His habit of "sinking his teeth into human flesh"—which started before he was a year old—became both more frequent and more damaging.

Adding further complication, Terrace became romantically involved with Petitto. (He had also been sexually involved with LaFarge but the relationship ended years before Project Nim.) After he "abruptly" ended the relationship, Petitto quit, cutting off Nim (again) from his closet companion and maternal figure. Terrace's two other full-timers quit around the same time. In the wake of these turnovers, Nim's behavior deteriorated further; he became more aggressive and less compliant with sign-language sessions.