The Mikveh is a traditional ceremonial immersion to restore a person to a status of being "clean". Traditionally it is done monthly for women. New converts to Judaism are also immersed.
In our Congregation, we recently had 3 young men and women undergo immersion. In a Messianic Congregation, this immersion is symbolic of dying to your old life, being buried with Messiah, and being raised with Messiah in new life.
It was an awesome celebration, over 80 attended. For pictures go to http://www.bethhamashiach.com/Baptism.htm. The tradition Is explained in detail, with it's Messianic meaning and associated Mitzvah (command) explained. For many of the congregation from a formerly Gentile background, it was their first experience with a Messianic Mikveh.