Since 1953 when the term "dietary fiber" was coined, there has been concern about accurately defining this macronutrient component of the human diet. Proper and adequate analytical methodology and food labeling regulations are dependent upon an accurate definition. Health impact studies also depend upon an accurate and meaningful definition along with relevant methodology to provide data of adequate quality for epidemiological and clinical studies. The scientific communities associated with dietary fiber within AOAC INTERNATIONAL have been the leaders in bringing consensus to the dietary fiber definition and method validation for over a quarter of a century. The consensus definition and subsequent methodology have served as the base for regulations worldwide with regard to dietary fiber labeling and health claims. Recently, there has been renewed interest in reviewing the dietary fiber definition and updating it if the review indicates such a need. The American Association of Cereal Chemists completed an effort that provides a continuum for the historical scientific and regulatory efforts while allowing for inclusion of future discoveries into a framework based upon the knowledge gained in the past. Such a definition will provide for transparent and workable regulations with regard to dietary fiber, and will allow the dietary fiber scientific community of AOAC to validate relevant methods. The Food Nutrition Board of the Institute of Medicine of the National Academies has published a set of definitions disconnected from the historical scientific base that do not provide a relevant basis for either adequate methodology, health studies or workable regulations.