Throughout our history, one of the central institutions of a Jewish community has been the mikveh.  Immersion in this ritual bath was required in Temple times in order to purify oneself after coming into contact with various types of tumah (ritual impurity).  Since then, the practical need for a mikveh has been relegated primarily to the laws of sex and conversion.  Yet the mikveh has taken on a greater significance in Jewish life than its specific halakhic applications would suggest.