The tradition of tossing the Bridal Garter dates back to 14th Century France. A tradition was started where the bride would "toss" her garter to the guests and the recipient would receive good luck and fortune. Nowadays, the groom tosses the garter to a group of unmarried men and whomever catches the garter is thought to be the next to marry.
The garter is typically placed on the bride's right leg above the knee. If a second garter is worn (one to throw and a second keepsake garter) they are both worn on the right leg with the tossing garter sitting just above the knee and the keepsake garter above the tossing garter. Many brides purchase blue garters as their "Something Blue" in the traditional good luck poem.