The Special Supplemental Nutrition Program for Women, Infants and Children (WIC) serves low- income pregnant, breastfeeding, or postpartum women, and infants and children up to age 5 who are at nutritional risk. In almost all States, the Program provides eligible recipients with vouchers that can be used at authorized stores—referred to as vendors. The 46,000 authorized vendors are mostly grocery stores and pharmacies which have signed agreements to follow program rules. In 1991 and 1998, FNS conducted national studies of WIC vendors to determine the extent of vendor violation of program rules. After the 1998 study, FNS issued regulations to correct vendor practices. The 2005 study replicates the 1998 study to determine whether the regulations were effective, and to measure the frequency of vendor violations and the degree to which vendors charge accurate prices for WIC transactions. It also provides data on payment error as required by the Improper Payments Information Act (IPIA) of 2002 (P.L. 107-300).