That would be Putnam's Who Moved My Cheese? by Spencer Johnson, which this week begins its second 100 weeks of bestselling tenure on PW's hardcover nonfiction list. Originally published back in September 1998 with a 95,000-copy first printing, the book is now at 5.5 million copies (92 printings) and has occupied our #1 slot 55 times.

With reporting by Dick Donahue.