This document provides documentation for the USDA Database for Flavonoid Content of Selected Foods, Release 2.1. It summarizes the procedures used to update the database with 168 new foods and additional compounds for some existing foods. Analytical values were obtained from USDA analysis of foods as well as from literature. Values are provided for 26 common flavonoid compounds in five subclasses. The database is presented in tables listing nutritional values for flavonoids in 385 foods, and is intended to be a resource for researchers, nutritionists and consumers.