灰色文献（Gray Literature）介于正式发行的白色文献，与不公开出版并深具隐密性的黑色文献之间，虽已出版但难依一般方式购得。

目前对灰色文献的定义多取1997年举行的「第三次国际灰色文献会议」中所提出「系指不经营利出版者控制，而由各级政府、学术单位、工商业界所产制的各类印刷与电子形式的数据。」

Grey literature (or gray literature) is a term used to refer to materials and research produced by organizations, outside of the traditional commercial or academic publishing and distribution channels. Common grey literature publication types include reports (annual, research, technical, project, etc.), working papers, government documents, white papers and evaluations. Organizations that produce grey literature include government departments and agencies, civil society or non-governmental organisations, academic centres and departments, and private companies and consultants.