Citizens owe allegiance to the state and are entitled to civil rights. Citizens are also required to defend the state by joining the military or to serve in other capacities. These duties vary by location.
In the case of U.S. citizenship, the Free Dictionary notes that loyalty is the most important obligation. This does not mean unyielding devolution to the state, but there must be some form of faith in the system. President Theodore Roosevelt proclaimed that each man must devote a reasonable portion of his time to politics in his community. The Administrative Office of the U.S. Courts mentions that jury duty is another duty of citizenship, but rights and freedoms are secured through collaboration between a jury and judge.
Wikipedia notes that governments, organizations and other individuals cannot suppress the political and civil rights of individuals. For example, the Free Dictionary adds that the rights of citizens of the United States are outlined in the Constitution. This document preserves a citizen's rights domestically, and it also provides protection when traveling to a foreign country.