Scientists need specific data on the amounts of vitamin D in foods and dietary supplements to facilitate the assessment of vitamin D dietary intake. This vitamin is available in foods both naturally and from fortification. The Nutrient Data Laboratory of the US Department of Agriculture (USDA) is collaborating with vitamin D experts to review and develop methods for analyzing the vitamin D content of foods and to use these methods to analyze the vitamin D content of certain foods and dietary supplements. In this article, we review existing sources of vitamin D data on foods and dietary supplements, describe the USDA's Dietary Supplements Ingredients Database, and discuss the development of the USDA's vitamin D database for foods. In addition, we define the challenges and needs related to providing updated data on the vitamin D content of foods and supplements. After we analyze the vitamin D content of these food samples, we will disseminate the current values in the National Nutrient Database for Standard Reference (Internet: http://www.ars.usda.gov/nutrientdata).