The NIH (National Institutes of Health) Guidelines on the Inclusion of Women and Minorities as Subjects in Clinical Research requires investigators applying for NIH research funds to develop and, if funded, implement plans for the inclusion of women and minority populations in their research, when that research involves human participants. It is the purpose of this article to help investigators understand (a) the scientific context and rationale behind the NIH Guidelines; (b) the NIH-defined concepts and the specific content of the NIH Guidelines; and (c) how the intent of the NIH Guidelines is related to mental health services research, the most applied area of mental health research. The article also discusses where investigators can find additional information as they work to implement the NIH Guidelines.