Airline alliances are partnerships between airlines worldwide. Most of the major airline carriers are part of one of three alliances: One World, Sky Team, or Star Alliance. Some airlines also have additional partners that are not in their overall alliance.

Airlines within an alliance may share flights, sell flights on a partner airline, and allow bookings across airlines within the alliance.

So what does this mean if you are booking with miles? That you have more options!

More airlines, more routes

Let's use United Airlines as an example. United Airlines is in the Star Alliance and through that has partnerships with airlines such as Asiana Airlines, ANA, and Lufthansa.

This mean that you can use United miles to book trips on United Airlines and also on any of their partner airlines as well.

It doesn't mean you can book any flight that is offered. Not all flights have available award seats, but this greatly opens up your options. This is particularly important for international flights. United Airlines, for instance, doesn't fly to the Philippines, but its partners Asiana and ANA do.

Keep in mind that when searching for award flights, not all available flights show up on the airline's website. If you're searching on United, all the United flights you could book with miles will show with their corresponding cost.

Some partner flights will show up as well. Often other partner flights are available that don't show up on the United or American sites.

One easy way to find more available routes is to use an award search tool like Seats.Aero or Pointsyeah.com (covered later in this course).

Using foreign airlines to book U.S. domestic flights

This also works in reverse — if you have miles with Turkish Airlines or Asiana or ANA, you can use them to book a flight within the U.S. on United, since they are partners through the Star Alliance.

Because each airline sets its own reward charts, it can be advantageous to transfer your reward points to a foreign airline with the intention of booking a flight on a US airline because the redemption value is better. You can find more information about this kind of sweet spot in our flight guides.