If you're retiring abroad, and you want to become a citizen of that country, it will take an investment of time or money, or both, to pull it off, but some countries require much less of either under certain circumstances. In fact, for some countries your heritage is far more important than your time or your assets.

Take two examples, Mexico and Ireland:

• Mexico requires most immigrants to live in the country for up to five years before applying for dual citizenship, but the wait is as little as two years if you are a direct descendant of someone born in Mexico or in any Latin or Iberian country.
• Ireland welcomes descendants home with open arms. If one of your grandparents was born in Ireland, just sign the Foreign Births Register and you're a citizen.

Many other countries ease citizenship requirements for people in special circumstances, most notably those who can prove their so-called blood ties. This usually means a shorter residency requirement, or none at all.

But you might still consider why you would want to be a naturalized citizen of another country, and whether permanent residency might do just as well.

Almost any country that you would want to live in welcomes American retirees, as long as they can prove that they have a certain minimum income from some combination of Social Security, a pension and investment income. It varies, and, reasonably enough, countries with a higher cost of living require a higher income.

Generally, there's a three-stage process, from tourist to resident to citizen, though the wait time and red tape differ in every country. The U.S. State Department keeps track of the specifics regarding short-term visits. The website of each nation's U.S. consulate is the best for facts on residency and citizenship requirements.

Here's how it works for most countries:

• An American with just a passport typically can stay in a foreign country for up to 90 days. Some expats stay on for years, taking a bus across the border and back again every three months to restart the clock. This is not a recommendation. A cranky border guard can make your life very difficult.
• Long-term stays generally require a residency visa, which may need to be renewed yearly for several years before permanent residency can be applied for and awarded.
• A citizenship application, in most countries, requires a longer period of residency, varying from as little as two years to as long as 10 years. Some have fast-track programs that cut the wait for people who make a substantial investment in the country.

All of the above is relatively straightforward in most countries for retirees, assuming they don't want to take a job and can prove they have a steady income. Relatively meaning that some countries make it tougher than others, with onerous requirements and plenty of paperwork.

And that raises the question whether you want to be a permanent resident or a citizen of your adopted country. The benefits and drawbacks vary for each country.

In any case, remember that neither dual citizenship nor residency gets you out of filing a U.S. tax return every year. It is both unusual and burdensome, but Americans have to pay income taxes wherever they live, and they owe it no matter where their income was earned. You may also have to file income tax to your country of residence, although most deduct the amount American residents pay to the U.S. (See How To Pay Taxes If You're Overseas.)

In case you're wondering, you can relinquish your U.S. citizenship, but that step is irrevocable and uncommon. In 2014, a whopping 3,415 did so, and that is an all-time record. According to Forbes.com, some were very wealthy Americans who found they could no longer hide assets in foreign bank accounts. Since a new U.S. law requires those deposits to be reported to the IRS, the banks either do so, or flatly refuse to do business with Americans. For the rest, the sheer aggravation of filing in two countries every year was a likely factor in their renunciation of U.S. citizenship.

The more common choice for a retiree expat is between permanent residency and dual citizenship. (See Advantages & Disadvantages Of Dual Citizenship.)

Which brings us to Panama, which may have the world's most enticing deal for American retirees. To qualify for Panama's Pensionado Visa Program, you need only to prove that you have a minimum lifetime income of $1,000 a month, or $1,250 for a couple. There isn't even a minimum age. Once you have your pensionado identity card, you can flash it to get a 50% discount on entertainment, 30% off on public transportation, 25% off airline tickets and more. The government even waives import taxes on the belongings you bring into the country. (For more, see 6 Reasons Why Americans Retire in Panama.)

Notably, the Pensionado program does not get you on a path to Panamanian citizenship. Panama has other visa programs that do, but they are aimed at entrepreneurs and investors.

The fastest track to dual citizenship can be to plant yourself in the soil from which your ancestors came. Unlike Ireland, some of these nations have narrowly defined programs, or bureaucratic barriers to deter the faint-hearted. Every nation has a website that details its requirements.

Here are a few examples of fast-track citizenship programs:

Israel: If you or your spouse is Jewish, by birth or conversion, you are eligible for citizenship.

Spain and Portugal: Spain has eased its dual citizenship requirements for descendants of any of the 300,000 Sephardic Jews who were expelled from that country during the Inquisition. Since that happened in 1492, we're talking about millions of people. Portugal has enacted a similar law.

Italy: You can apply for citizenship by descent if a grandmother or grandfather was an Italian citizen. Even a great-grandfather will do, but not a great-grandmother. As that fact implies, Italy's requirements are confusing, and its bureaucracy is legendary.

Germany: Germany has a program that awards citizenship to descendants of Germans who were deprived of their citizenship for political, racial or religious reasons when the Nazis were in power, between 1933 and 1945.

Note that citizenship in any European country has a side benefit: It gains you certain rights as a citizen of a European Union member nation. (See also: Developed Countries For Easy Residency/Citizenship.)

American retirees who have a regular income are welcome in most countries, and most will smooth your path to permanent residency. Full citizenship usually takes a greater investment of time and effort. Unless, that is, you want to retire to the country that your ancestors called home.

See also: 5 Hardest Countries For Getting Citizenship