Dual nationality means that a person holds citizen of two countries at the same time. Each country has its own citizenship laws. The United States recognizes the concept of dual citizenship. Other countries have their own rules relating to dual citizenship and those rules can change over time. At this time both Canada and Mexico permit their citizens to be dual citizens of the United States.
Information on losing foreign citizenship can be obtained from the foreign country’s embassy and consulates in the United States.
Americans can renounce U.S. citizenship in the proper form at U.S. embassies and consulates abroad.