International Tipping Customs
Michael Lynn, an associate professor of market and consumer behavior at Cornell University School of Hotel Administration, researched the variations of tipping in different countries. Comparing the types of services that were tipped in each country with personality tests that had been given to people in those countries, he came to the conclusion that countries with more extroverted and neurotic people gave tips to the greatest number of services and also tipped the largest amounts. (The U.S. was at the top of both of those categories, by the way.) His theory is that "extroverts are outgoing, dominating, social people" and see tipping as an incentive for the waiter to give them extra attention. Neurotics are more prone to guilt and general anxiety, making them tip more because of their perceived difference in status between themselves and the server.
Aside from these facts, other cultures definitely see tipping differently. For example, in many European restaurants, 10% to 15% has already been added to the restaurant bill. You can leave extra if the service was especially good, but it isn't usually necessary. In Australia and New Zealand, tipping is frowned upon -- virtually non-existent. In South Africa, you'll be expected to tip almost everyone.
Visit the tipping guidelines page at Global Assignment: Americans Abroad or BBC: International Tipping Etiquette for specific information about the varied tipping customs around the world.
For more information on tipping and related topics, check out the links on the next age.