In Jewish law, or Halachah marriage is a contractual relationship between husband and wife, but it is not a contract between equals. With the ketubah the husband makes a contract with his wife outlining his obligations towards her. The marriage is ended only by death or dissolution of the marriage on the part of the husband by presenting his wife with a get, or bill of divorce. The penalties for remarrying without the get weigh more heavily upon the wife than on the husband.
In the event the husband abandons his wife, is missing in action, is incapacitated or refuses to give his wife a get, the wife becomes an agunah, or "chained wife". Under Jewish law, an agunah is still legally married, even though she may have a civil divorce. As an agunah she may not remarry. If she does remarry it is considered adultery and any child as a result of such a union is illegitimate, a mamzer, only eligible to marry converts or other mamzen. Furthermore, all their descendants are mamzen. Even if her ex-husband later gives her the get, her subsequent adulterous remarriage is not legitimized.
Essentially the agunah is in a state of marital limbo; she has little to no recourse to legally end her marriage. A vindictive husband, or one who is merely holds out hope for a reconciliation, can keep an agunah waiting for years for her get, blackmailing her and her family for money or for custody relationships. In Israel some men will even serve jail time before giving their wives a get. Many agunah fear the rabbinical courts will rule in favor of their husbands, are disinclined to turn to them for resolution. Fortunately there are organizations that work to settle divorce disputes within Jewish law and allow agunahs to get on with their lives.