A United States patent provides rights only within the United States against infringers, including the right to prevent importation of products into the U.S. made by a patented process. If you expect substantial foreign sales or foreign competitors, you may consider obtaining a patent in one or more foreign countries.
Foreign patent protection can be very expensive since there is the need eventually to file your patent application in each country and file translations into the appropriate language.
There are procedures where you can initially file an international application under the Patent Cooperation Treaty in which a search and preliminary examination are performed initially prior to entrance into a regional or national phase.
Using this procedure allows you to delay the decision as to the countries in which the application will be filed. Your patent attorney can provide much more guidance regarding foreign patent application procedures.
Any publication, public use or disclosure prior to your filing date may bar you from obtaining a foreign patent. It is often advisable to file the foreign patent application within one year after the filing of the U.S. patent application (including a provisional application).
A license must be obtained from the USPTO to file your patent application in a foreign country unless more than six months have passed since your US filing date (unless the USPTO has informed you otherwise).