Live in the U. S.65 or older: Tricare 4 Life (supplement to Medicare which is primary) https://tricare4u.com/apps-portal/tricareapps-app/static/
Under 65: Tricare is primary and you choose which package you want (Tricare Standard, Prime, etc.) http://www.tricare.mil/
Live Outside the U. S.Any age: Tricare Standard is the only one you can get outside of the States and it is primary (since Medicare applies only in the States). You pay up front for your medical costs, and then get reimbursed.
Here is information of how we get reimbursed for our medical expenses while living in Ecuador:Since we are outside of the U.S., the only choice in Tricare coverage is Tricare Standard. Medicare doesn't work here, so Tricare Standard is primary. We pay the medical bills and prescription costs ourselves and then submit the claim form to receive reimbursement. The claim form is DD Form 2642 and can be found on the following website: http://www.tricare.mil/Welcome.aspx. You fill it out online, (don't forget to save to your computer if you wish), print the completed form, sign it, attach the backup doctor statements/receipts, and mail to the following address.
P. O. Box 7985
Madison, WI 53707-7985
(I mail everything in one large manila envelope from the post office here.) It takes about two months to get the EOB with the reimbursement checks mailed back to me at our P. O. Box here, which I deposit in our bank account here.
You generally get reimbursed about 75% of the medical expenses after your deductible has been met. (My husband had emergency gallbladder surgery in Cuenca in 2011 which came to $2,200.00 at Monte Sinai, and we got reimbursed 75% of it.) It's not as good as having dual coverage (Medicare and Tricare) because then we don't have to pay anything, but it's better than not having any coverage at all (and we don't pay any premiums, only deductibles and cost-shares).
Hope this information helps those military retirees and their spouses who are thinking of retiring overseas.