Does Medicare provide coverage as we travel outside of the United States?

In general, no. Medicare Part A (inpatient care) and Medicare Part B (out-patient) coverage is usually not covered as you travel outside the United States or U.S. Territories including: American Samoa, Guam, the Northern Mariana Islands, Puerto Rico ("Estado Libre Asociado de Puerto Rico"), and US Virgin Islands.

However, as noted by the Centers for Medicare and Medicaid Services (CMS): "Medicare may pay for inpatient hospital, doctor, ambulance services, or dialysis you get in a foreign country in these rare cases:

You are in the United States when a medical emergency occurs, and the foreign hospital is closer than the nearest U.S. hospital that can treat your medical condition.
You are traveling through Canada without unreasonable delay by the most direct route between Alaska and another state when a medical emergency occurs, and the Canadian hospital is closer than the nearest U.S. hospital that can treat the emergency.
You live in the U.S. and the foreign hospital is closer to your home than the nearest U.S. hospital that can treat your medical condition, regardless of whether an emergency exists.
In some cases, Medicare may cover medically necessary health care services you get on board a ship within the territorial waters adjoining the land areas of the United States. Medicare won't pay for health care services you get when a ship is more than 6 hours away from a U.S. port."

(source: https://www.medicare.gov/coverage/travel now offline. See: https://www.medicare.gov/coverage/travel-outside-the-u.s.)

For more information about what Medicare may cover as you travel outside the United States, please contact a Medicare representative at 1-800-633-4227.

Medigap policies and International healthcare coverage

Some Medicare Supplements (Medigap) plans may provide some emergency international healthcare coverage or allow you to purchase additional riders for foreign coverage. You may find that a Medigap policy will only pay a percentage of your foreign coverage (such as 80%) - and may have a $50,000 lifetime benefit - and a separate foreign travel coverage deductible (such as, $250). In addition, your Medigap coverage may only apply for the first 60 days of each trip you make outside of the United States. You can contact your Medigap provider or insurance agent. You can also check your Medigap policy documentation (for example in Plan D, G (high-deductible), M, N - and Plans C and F for people eligible before 2020) for foreign travel emergency coverage or coverage in a foreign country (with possible foreign deductible and plan limits applying).

See also: https://www.medicare.gov/health-drug-plans/medigap/basics/coverage

Supplemental travel insurance coverage

If you do not have a Medigap policy that provides foreign travel emergency coverage (or you have already met your $50,000 lifetime foreign travel emergency coverage limit), you may wish to consider buying a travel insurance policy that includes health coverage. Travel health insurance may include some limitations or deny claims for pre-existing conditions. You can speak with your travel agent or insurance agent about your healthcare options as you travel abroad.

A note on Medicare Part D vaccines before traveling outside the United States.

Medicare Part D covers all vaccines recommended by the Advisory Committee on Immunization Practices (ACIP) at a $0 copay. This includes any vaccines you may need before traveling outside of the United States (CMS notes the examples: yellow fever, chikungunya, and Japanese encephalitis).