NIMBY (English pronunciation: /nɪːmbiː/, or nimby), an acronym for the phrase "not in my back yard", is a characterization of opposition by residents to proposed developments in their local area, as well as support for strict land use regulations. It carries the connotation that such residents are only opposing the development because it is close to them and that they would tolerate or support it if it were built farther away. The residents are often called nimbys, and their viewpoint is called nimbyism. The opposite movement is known as YIMBY for "yes in my back yard".

Some examples of projects that have been opposed by nimbys include housing development, homeless shelters, solar farms, incinerators, sewage treatment systems, fracking, and nuclear waste repositories.