Does a U.S. trademark registration protect a trademark in a foreign country?

No. Trademarks are territorial and must be filed in each country where protection is sought. However, if you are a qualified owner of a trademark application pending before the U.S. Patent and Trademark Office (USPTO), or of a registration issued by the USPTO, you may seek registration in any of the countries that have joined the Madrid Protocol by filing a single application, called an "international application," with the International Bureau of the World Property Intellectual Organization (WIPO), through the USPTO.  As of June 9, 2011, U.S. applicants can concurrently seek protection in up to 84 countries. More information on filing an international application under the Madrid Protocol, visit the USPTO website.

To file with a specific country, check WIPO’s list of international trademark offices here. Make sure to consider registering transliterations (representations of words in the corresponding characters of another alphabet) when making trademark decisions. For example, foreign entities may trademark the name of your company written in their alphabet to make a transliteration of you trademark that they then trademark for themselves.