Puerto Rico is a commonwealth of the United States. However, in practice, Puerto Rico technically is not a commonwealth. A commonwealth is defined as a nation, state or other political unit where "supreme authority is vested in the people." (Source) While Puerto Rico has its own constitution, judiciary, legislature and governor, in a recent decision the Supreme Court determined that the ultimate source of sovereignty over Puerto Rico is the U.S. Congress (Source). People born in Puerto Rico are U.S. citizens, they pay into Social Security and Medicare, but they cannot vote for President and cannot vote on legislation in the U.S. Congress. Although Puerto Rico is a "commonwealth" on paper, the practical realities are far more complicated. (Source)