One difficulty of traveling abroad is knowing when to tip and how much. Different countries have different customs. In some places a tip not only is urged, but is expected. In others, a tip is an insult. American Express recently offered this rundown on what to do and where to do it:

London: Unless a service charge is on the check, tip 10 to 15 percent at hotels and bars. The same to taxi drivers, but smaller amounts to porters, doormen and other attendants.Paris: Look for the words "service compris" on bills, which means the tip has been included in the check. If it is not there then add 8 to 12 percent of the bill. Also a few francs to the cloakroom attendants, tour guides and doormen. Air and rail porters charge by the item. In taxis, tip 10 to 15 percent.

Italy: Hotels and restaurants usually add 15 percent. Waiters expect a little more. Taxis should get 10 percent.

Greece: A 10 percent tip is shared by the staff in better restaurants and bars.

Canada: Fifteen percent in restaurants, 10 to 15 percent to cab drivers. Bellhops get 50 cents to $1 per bag. Leave a dollar per day for maid service.

Germany: If the bill says "bedienung" it means the tip has been added already. If not, add 10 to 15 percent. Round up to the nearest mark for taxis. Bellhops get 50 cents to $1.

China: Tips are not acceptable under any circumstances.

Australia: Tipping is not customary and isn't expected. Waiters are the exception, 10 to 15 percent.

Mexico: When in doubt, leave a tip. Restaurants should get 10 to 15 percent. Taxi drivers should get small change.

Hong Kong: Restaurants usually include 10 percent on your bill. Washroom attendants get one or two Hong Kong dollars. Small change for taxis.

Japan: Tips are not expected. Hotels and good restaurants add up to 15 percent.