The minimum legal drinking age refers to that age at which consuming an alcoholic beverage is permitted by law. This may differ from the minimum age at which one can purchase alcohol -- Indonesia, for example, focuses only on a minimum legal purchasing age.

Some consider the legal drinking age an arbitrary age restriction that promotes alcohol abuse in much the same way as prohibition did in the United States.

International Minimum Drinking and Purchasing Age Laws

Argentina
Minimum Legal Drinking Age: 18
Minimum Legal Purchasing Age: -
Australia
Minimum Legal Drinking Age: 18
Minimum Legal Purchasing Age: 18

State and Territory laws prohibit the sale or serving of alcohol to those under 18.

Austria
Minimum Legal Drinking Age: -
Minimum Legal Purchasing Age: 16, 18 in some cases for spirits.

On-premises consumption of alcohol is subject to provincial regulation. In general, the MDA is 16. Some provinces also prohibit the consumption of spirits for those under 18.

Azerbaijan
Minimum Legal Drinking Age: No MDA
Minimum Legal Purchasing Age: No MPA
Belgium
Minimum Legal Drinking Age: 16
Minimum Legal Purchasing Age: 16

The law prohibits anyone under 16 (unless married or accompanied by a parent or guardian) from entering a 'dance hall' where fermented beverages are sold.

Brazil
Minimum Legal Drinking Age: 18
Minimum Legal Purchasing Age: -
Canada
Minimum Legal Drinking Age: In Alberta, Manitoba and Quebec, it is 18; in all other provinces, 19
Minimum Legal Purchasing Age: All provinces have their own legal MPA.

Drinking by minors under adult supervision is permitted in licensed premises in provinces of Manitoba and New Brunswick and at home in Prince Edward Island, Alberta, British Columbia, Ontario and Saskatchewan.

Chile
Minimum Legal Drinking Age: 18
Minimum Legal Purchasing Age: -
China
Minimum Legal Drinking Age: No MDA
Minimum Legal Purchasing Age: -
Colombia
Minimum Legal Drinking Age: 18
Minimum Legal Purchasing Age: -
Czech Republic
Minimum Legal Drinking Age: 18
Minimum Legal Purchasing Age: -
Denmark
Minimum Legal Drinking Age: -
Minimum Legal Purchasing Age: 18

There are no age restrictions on sales for off-license consumption.

Estonia
Minimum Legal Drinking Age: 18
Minimum Legal Purchasing Age: -
Finland
Minimum Legal Drinking Age: 18
Minimum Legal Purchasing Age: 18, 20

The MDA for on-premises consumption of all alcoholic beverages is 18; for off-premises consumption the MPA for beverages up to 21% alcohol by volume is 18. The MPA for spirits is 20.

France
Minimum Legal Drinking Age: 16
Minimum Legal Purchasing Age: 16
Georgia
Minimum Legal Drinking Age: No MDA
Minimum Legal Purchasing Age: No MPA
Germany
Minimum Legal Drinking Age: 16, 18
Minimum Legal Purchasing Age: 16, 18

The MDA and MPA for beer and wine is 16, 18 for spirits.

Hong Kong
Minimum Legal Drinking Age: 18
Minimum Legal Purchasing Age: No MPA
Hungary
Minimum Legal Drinking Age: 18
Minimum Legal Purchasing Age: -
Iceland
Minimum Legal Drinking Age: 20
Minimum Legal Purchasing Age: -
Indonesia
Minimum Legal Drinking Age: -
Minimum Legal Purchasing Age: 16
Ireland
Minimum Legal Drinking Age: 18
Minimum Legal Purchasing Age: 18

Individuals under 18 are allowed in bars, but those under 15 must be accompanied by a parent or guardian.

Israel
Minimum Legal Drinking Age: 18
Minimum Legal Purchasing Age: -
Italy
Minimum Legal Drinking Age: 16
Minimum Legal Purchasing Age: 16
Japan
Minimum Legal Drinking Age: 20
Minimum Legal Purchasing Age: 20
Korea (South)
Minimum Legal Drinking Age: 21
Minimum Legal Purchasing Age: -

21 years of age; or a college student, if under 21.

Latvia
Minimum Legal Drinking Age: 18
Minimum Legal Purchasing Age: -
Lithuania
Minimum Legal Drinking Age: 18
Minimum Legal Purchasing Age: -
Luxembourg
Minimum Legal Drinking Age: 17, 18
Minimum Legal Purchasing Age: 18

The on-premises MDA is 17 if accompanied by an adult.

Malaysia
Minimum Legal Drinking Age: 21
Minimum Legal Purchasing Age: -
Mexico
Minimum Legal Drinking Age: 18
Minimum Legal Purchasing Age: -
Moldova
Minimum Legal Drinking Age: 18
Minimum Legal Purchasing Age: 18
Mongolia
Minimum Legal Drinking Age: 18
Minimum Legal Purchasing Age: 18

Parents and guardians may not offer alcohol beverages to their children under 18.

Netherlands
Minimum Legal Drinking Age: -
Minimum Legal Purchasing Age: 16, 18

The MPA for spirits is 18, 16 if accompanied by an adult. The MPA for beer and wine is 16.

New Zealand
Minimum Legal Drinking Age: 20 (with some exceptions)
Minimum Legal Purchasing Age: 20 (with some exceptions)

In designated areas alcohol may be sold to those between 18 and 20 who are having a meal or are accompanied by their parent, guardian, or spouse aged over 20.

Norway
Minimum Legal Drinking Age: 18, 20
Minimum Legal Purchasing Age: 18, 20

The MPA for spirits is 20. For beer and wine the MPA is 18.

Peru
Minimum Legal Drinking Age: 18
Minimum Legal Purchasing Age: -
Poland
Minimum Legal Drinking Age: -
Minimum Legal Purchasing Age: 18

The MPA for alcoholic beverages (more than 4.5% alcohol by weight) is 18. There is no minimum purchasing age for beverages under 4.5% ABV.

Portugal
Minimum Legal Drinking Age: No MDA
Minimum Legal Purchasing Age: No MPA
Russia
Minimum Legal Drinking Age: -
Minimum Legal Purchasing Age: 21
Slovak Republic
Minimum Legal Drinking Age: 18
Minimum Legal Purchasing Age: -
Slovenia
Minimum Legal Drinking Age: 18
Minimum Legal Purchasing Age: 18

Applies only to buying or drinking in public places such as bars or discos.

South Africa
Minimum Legal Drinking Age: 18
Minimum Legal Purchasing Age: 18
Spain
Minimum Legal Drinking Age: 16
Minimum Legal Purchasing Age: 16

Those under 16 may purchase beer and wine if accompanied by their parents.

Sweden
Minimum Legal Drinking Age: 18
Minimum Legal Purchasing Age: 18, 20

Class 1 beer is non-alcoholic and no age restrictions apply. Off-license purchases have different age limits, the MPA for buying beer from food stores is 18, the MPA for buying other alcohol beverages at Systembolaget stores is 20.

Switzerland
Minimum Legal Drinking Age: 14-18
Minimum Legal Purchasing Age: 14-18

Federal law prohibits supplying spirits to those under 18. The MDA and MPA for beer and wine is controlled by the Cantons and varies between 14 and 16.

Thailand
Minimum Legal Drinking Age: No MDA
Minimum Legal Purchasing Age: -
Turkey
Minimum Legal Drinking Age: -
Minimum Legal Purchasing Age: 18
Turkmenistan
Minimum Legal Drinking Age: 18
Minimum Legal Purchasing Age: 18
Ukraine
Minimum Legal Drinking Age: 21
Minimum Legal Purchasing Age: 21
United Kingdom
Minimum Legal Drinking Age: 18
Minimum Legal Purchasing Age: 18

In bars and off-licensed premises the MDA and MPA are 18. The MPA for beer and cider is 16 when purchased for consumption with meals (except when in a bar). Children over five may consume alcoholic beverages at home with a parent's consent. Further exploration (thanks, BlueDragon) uncovered that children over five may also consume alcohol in registered clubs and may consume (but not buy) alcohol ancillary to a meal in licensed premises.

United States
Minimum Legal Drinking Age: 21*
Minimum Legal Purchasing Age: 21**

*In 19 states alcohol consumption by youth under 21 is not specifically illegal.**Exceptions to the 21 law in some states include possession for religious purposes when accompanied by a parent, spouse or legal guardian; medical reasons; in private clubs or establishments; and in the course of lawful employment by a duly licensed manufacturer.

Uruguay
Minimum Legal Drinking Age: 18
Minimum Legal Purchasing Age: -
Venezuela
Minimum Legal Drinking Age: 18
Minimum Legal Purchasing Age: -
Please, by all means, /msg me if this list is inaccurate or incomplete.

Source:

ICAP Reports 4, March 1998 -- Drinking Age Limits:
http://www.icap.org/publications/report4.html