More Americans are choosing to retire earlier, and many are deciding to spend their retirement years outside the United States.

But where are they going? Cost of living, health care, and access to transportation are among the biggest considerations when choosing a destination.

The most popular country for retirees is Portugal, followed by Ireland and Spain. A newer entrant on the list is Malta.

One important caution: some countries require a significant financial investment over a period of years before granting residency.