The superstition that a Groom must not see his Bride before the wedding stems from the days of arranged marriages where the groom may never have seen his Bride. There was the chance that if he saw her before the ceremony, he might bolt! Hmm- wonder if the movie Runaway Bride took a modern twist on this one! Other sources say that to see the Bride in her dress was to peer into the future, which could bring bad luck to the union. Today it is thought very traditional to still wait until the aisle to see each other. Often now, with modern photography, a key snapshot is the initial meeting of the Bride and Groom in and intimate location before the ceremony.
Source: Random Facts (RandomHistory.com)