For those who are new to the idea of a marriage certificate, it's often a fairly large document (about 22 x 30 inches in this case) on which the couple's vows are written in calligraphy. The bride and groom sign it during or immediately after the wedding.
Guests may also sign as a commitment to support the couple in their marriage. Originally a Quaker tradition, marriage certificates can be an alternative to the traditional guest book. A nice advantage is that the art piece can be framed and hung in the couple's home as a special remembrance of the day.
And totally unrelated to this post, but too wonderful not to share... Thursday Quick Picks on PaperCrave led me to Kelli Anderson's The Human Body, a video that aims to teach children about body functions. She cut all of the parts from paper; even the sound effects are paper! See behind the scenes shots on Kelli's blog.