Since its origins in 18th-century English pubs, tipping has become a custom involving numerous professions and billions of dollars. Knowledge of the psychological factors underlying tipping would benefit service workers, service managers, and customers alike. Two studies were conducted to provide such knowledge about restaurant tipping. The percent tipped in these studies was related to group size, the customer's gender, the method of payment (cash or credit), and in some cases, the size of the bill. Tipping was not related to service quality, waitperson's efforts, waitperson's gender, restaurant's atmosphere, or restaurant's food.