In this paper I use a unique and rich data set on prices and promotions from major US supermarkets to examine the nature of National Brand and Private Label interaction. Private labels are priced and promoted competitively with NBs, in a manner suggesting that retails are careful not to lose private label market share during times of national brand promotions. The price margin between the two types of products continues to fall in US supermarkets, and the major determinants of the price differences between the two are promotional frequency and market concentration.