A non-U.S. entity that obtained a United States trademark registration without actually using the mark in the U.S. must still use its mark here to keep the registration active. A quirk of foreign treaties is that a non-U.S. entity can obtain a U.S. registration without having used the mark in the U.S. While this is an initial benefit to a foreign entity, the registrant must ultimately use the mark in the U.S. for the goods and services registered. Otherwise, a third party could challenge the registration as being abandoned, or the registrant would not be able to file documents to keep the mark active as required before the sixth year anniversary of the registration date and every ten year anniversary. Use in commerce is the foundation of trademark protection in the U.S., so non-U.S. registrants who benefitted from Section 44(d) of the Lanham Act or the Madrid Protocol should maintain relevant U.S. business if they want to keep their registrations active. For third parties searching the availability of trademarks, when a mark is registered on the basis of Section 44(d), look deeper to see if that foreign entity is actually using the mark, or if the registration can be cancelled due to non-use.