The Healthy Eating Index (HEI) is a measure of diet quality as specified by Federal dietary guidance, and publication of the Dietary Guidelines for Americans 2005 necessitated its revision. An interagency working group based the HEI-2005 on the food patterns found in My-Pyramid. Diets that meet the least restrictive of the food-group recommendations, expressed on a per 1,000 calorie basis, receive maximum scores for the nine adequacy components of the index: total fruit (5 points), whole fruit (5 points), total vegetables (5 points), dark green and orange vegetables and legumes (5 points), total grains (5 points), whole grains (5 points), milk (10 points), meat and beans (10 points), and oils (10 points). Lesser amounts are pro-rated linearly. Population probability densities were examined when setting the standards for minimum and maximum scores for the three moderation components: saturated fat (10 points), sodium (10 points), and calories from solid fats, alcoholic beverages (ie, beer, wine, and distilled spirits), and added sugars (20 points). Calories from solid fats, alcoholic beverages, and added sugars is a proxy for the discretionary calorie allowance. The 2005 Dietary Guideline for saturated fat and the Adequate Intake and Tolerable Upper Intake Level for sodium, expressed per 1,000 calories, were used when setting the standards for those components. Intakes between the maximum and minimum standards are pro-rated. The HEI-2005 is a measure of diet quality as described by the key diet-related recommendations of the 2005 Dietary Guidelines. It has a variety of potential uses, including monitoring the diet quality of the US population and subpopulations, evaluation of interventions, and research.