There are a huge number of traditions within a wedding ceremony. In fact, just about every action is indicative of some kind of tradition, and as such, almost everything is filled with symbolism and import. This is particularly true of the lighting of the unity candle. Unity candles are relatively new in the world of weddings, and their use remains most popular in the United States. But this ceremony very clearly represents the joining of two separate entities into one stronger end result.
A unity candle ceremony starts by one representative of each family lighting a tapered candle. These representatives are usually the mother or father of the bride and groom. Then after the formal vows have been exchanged, the bride takes a lit pillar candle and the groom takes his lit pillar candle, and they use these smaller pillar candles to light a larger candle in the middle of the table. Some couples choose to save the unity candle and relight it on their anniversaries.