Ladies On The Left Arm of the Gentleman The tradition goes back to Medieval times. The knights lady was always on his left arm to protect her. Traditionally, the bride stands on the left, the groom on the right. (Although the Jewish wedding tradition reverses this.) Weddings used to be a lot more like the ones you watch on daytime TV, with dastardly ex-suitors and other thugs sometimes rushing the altar! And, of course, some wedding crashers were heroes, just trying to rescue a captured bride. Whatever the reason for the interference, the groom needed to keep his right hand free so he could grab his sword, thus the bride stood clear and to the left.

via Taylored Weddings