Airlines know the price of getting a new customer. And they know that its a whole lot easier and less expensive to keep the customers that they already have. For this reason, airlines started frequent flyer programs. These programs reward you the more you fly.

Frequent flyer programs let you to receive certain travel benefits based on the number of miles (or sporadically the number of trips) you fly on a specific airline. Standard awards include a free ticket or a free upgrade from coach to first class.

Some airlines also offer "elite" programs that provide check-in and boarding priorities, and "affinity" credit cards which earn mileage credits when you use them for purchases. In order to earn these benefits you must become a member of that airlines program; this can often be done through a travel agency.

There isnt a how many programs you can join. But before you decide which program to join, you should compare different programs carefully.

Every airline program carries conditions and limitations. So you should be careful to read the promotional material and the all the fine print. Here are a few things you should take a look at:

- The rate at which credits are earned, minimum credits earned per flight

- If you are more interested in free tickets for yourself, or companion tickets, or upgrades

- How much credit you need for the awards youre interested in

- What are the deadlines for accumulated credits?

- Does the airline serve the cities youre traveling to, and if it has tie-ins or other airlines and to car rental companies and hotels you would use.

- If awards can be transferred to someone else or just members only

Also, airlines reserve the right to make changes at any time. More often than not, without notice. This can include changes to the conditions and limits on the awards earned.

You should also be keeping track of the mileage you've earned and check it against the statement the airline mails to you.

It's not uncommon that airlines add new routes after you join the program.You might be able credits on that route but not use awards there.

Another important not that you should be aware of is that airlines usually restrict the transfer of mileage earnings. Most often being the sail or attempted sale of credits or awards you've earned and want to sell. You should never try this as the airlines have caught on to these schemes and actively persue it.