Countries usually frame their citizenship laws with little or no regard for the citizenship laws of other countries. For example, a child born to US citizen parents in a foreign country may be both a US citizen as well as a citizen of the country of birth.

Citizens of dual nationalities owe their allegiance to both the countries and either country has the right to enforce its laws, particularly when the person traveling there. Dual nationals may also be required by the foreign country to use its passport to enter and leave that country.
Newly naturalized citizens may be required to renounce their previous citizenship(s). The US has such a requirement but Canada does not. In some cases, a country will automatically revoke the citizenship of one of its citizens who acquires another country's citizenship by naturalization, even if no explicit renunciation was involved.

Citizenship laws are framed with little consideration for the citizenship laws of other countries. Certain countries restrict dual citizenship by requiring naturalized citizens to renounce the other citizenship upon attaining adulthood. Certain countries automatically revoke the other citizenship of the naturalized citizen albeit no renunciation is involved. Though advantages of dual nationality are many, there are certain sticky legal issues, which should be thought of prior to acquiring double citizenship.

Dual citizens are generally not entitled to any special treatment by either of the two countries. Each country will consider you to be a citizen of that country alone. This might lead to certain undesirable situations. Citizenship of any country usually carries with it certain legal obligations. A dual citizen has to owe allegiance and obey laws of both countries. Both countries have the right to enforce its laws.

A dual citizen may sometimes be expected to pay taxes in a country he does not live, be liable to drafted in the military, and ban on visiting certain countries including the country in which he is a citizen.