Bestsellers are harder to track than you'd think and it's not easy for everyone to agree which are the biggest. Each bestseller list--The New York Times, USA Today, BookScan, local newspapers--is calibrated slightly differently. We decided to partner with Nielsen BookScan to chart the biggest bestsellers of the first decade of the new millennium. Yes, we know that they only started keeping track in 2004, but when we compared our lists--gathered by analysis of a decade of bestseller lists and consensus--to Bookscan's list of the top 20 (fiction, non-fiction, adult, children, hardcover and trade paperback), they were very close. In order of rank, here's the list. Did you read them? Which were your favorites?