No other section of the supermarket offers as many choices as the wine aisle. A typical retailer is likely to have hundreds of unique wines on its shelves. Just three firms, however, account for more than half of the wine sales in the United States. What impact does this industry concentration have on consumer choices? To answer this question we conducted an inventory of wine offerings at 20 retailers in Michigan. We recorded more than 3,600 unique varieties of wine, and traced their relationships with more than 1,000 different firms.