Supermarkets evolved in the 1920s and 1930s. For example, Piggly Wiggly Food Stores, founded by Clarence Saunders around 1920, introduced self-service and customer checkout counters. Supermarkets are large, self-service stores with central checkout facilities; they carry an extensive line of food items and often nonfood products.
Supermarkets were among the first to experiment with such innovations as mass merchandising and low-cost distribution methods. Their entire approach to the distribution of food and household cleaning and maintenance products was to make available to the public large assortments of a variety of such goods at each store at a minimal price.