Who should you tip? How much is appropriate? How should a tip be offered? Situations that may call for gratuities always seem riddled with questions. When in doubt, we try to err on the side of generosity.

Scenario: Hotel's concierge to make restaurant reservations, purchase theater tickets for you, and tell you where the nearest Tube stop is.

Download our handy, printable tipping guide to 10 popular countries. If you don't already have it, you will need Adobe Acrobat, a free (and easy!) plug-in, to read the guide Download the Tipping Guide Download Adobe Acrobat FEBRUARY 2006 ISSUE • Table of Contents • Secret Hotels of Costa Rica • Europe on the Quick: A Long Weekend in Stockholm • Pacific Coast Highway • Trip Coach: Spain, Portugal, and the Azores • Shut Up and Ski • 40 Best Vacations

How Much To Tip--And Why: $20. Most tasks that a concierge handles (arranging show tickets, excursions, dinner reservations, or babysitting) call for a tip, and in pricey London, $10 per request is fair. There's no need to tip for quick inquiries about the nearest Tube stop or what street offers prime window-shopping. You might up the gratuity if you're staying for an extended period and want to be in the concierge's good graces. Also, it's common to tip more at high-end hotels.

Scenario: A waiter in Sydney brings free wine samples and steers you away from the halibut in favor of the yellowfin tuna, which turns out to be fantastic. The bill is about $60.

How Much To Tip--And Why: $6. Service fees are rare Down Under, and waiters, maids, taxi drivers, and even tour guides don't expect gratuities. Still, nowadays patrons at restaurants and cafés commonly tip waiters 5 to 10 percent of the bill when service is excellent. If the food and service were merely adequate, hold the tip, or round up the bill by $1 or $2. On the other hand, you might tip even more if the waiter threw in a dessert or a round of drinks.

Scenario: The bill for an uneventful taxi ride from the airport to your hotel in downtown Buenos Aires comes to a little less than $20.

How Much To Tip--And Why: $2. Locals usually don't tip taxi drivers, but, after years of experience with North American tourists, cabbies throughout South America have come to expect a small gratuity from foreigners. Rounding up the fare and telling the driver to keep the change is fine; there's no need to give more. For that matter, tipping the driver is by no means necessary, so don't do it if the service isn't satisfactory.

Scenario: Dinner at a Munich bistro costs $25. Your waitress was decent but not extraordinary.

How Much To Tip--And Why: $2. Waitstaff in Europe don't rely on tips the way their American counterparts do. Still, patrons on the Continent often tip one or two euros and change for good service. This is the case in France and Italy, where a service fee is usually marked on the bill (as service compris and servizio repectively), and in Germany and Austria, where the gratuity may not be spelled out. (In Germany and Austria, don't leave money on the table; hand it to your server.)

Scenario: While on a weeklong Caribbean cruise, your cabin is well taken care of by housekeeping, with beds made and towels replaced in a timely and unintrusive fashion.

How Much To Tip--And Why: $0. Cruise ships almost always add a gratuity to the bill. For the rare situation when a tip's not figured in, give the amount that most ships automatically charge: $10 per person per day. Even if the tip is tacked on, passengers usually have the power to change the amount. The staff counts on the money as part of their income, so request that the gratuity be removed only if the service was exceptionally poor--and explain to the management why you were disappointed.

Scenario: During your five-day safari in Kenya, the driver and guide were adequate but at times a bit curt--and you didn't see all the animals you had hoped to.