The Ketubah, literally "that which is written," is the Jewish marriage contract. The Ketubah is one of oldest continuously used elements of Jewish marriage rites, dating from the Talmudic era. Traditionally written in Aramaic, the language of the Talmud, the Ketubah outlines the groom's obligations to the bride for food, clothing and conjugal rights, provides safeguards for the bride against arbitrary divorce and details the settlement she is to receive should the marriage be dissolved either through death or divorce. Essentially, the Ketubah is the world's oldest pre-nuptial agreement, specifically protecting the rights of the wife. After being signed by two witnesses, it becomes the wife's property and is recognized by rabbinical courts.
Although the wording of the Ketubah was standardized by the Middle Ages, couples did and continue to personalize their Ketubahs, inserting clauses of specific concern, whether serious or whimsical. For example, my brother-in-law's ketubah with his wife specifies that he will take her dancing once a year. Interestingly, though the Ketubah is written in Aramaic, the date is written in Hebrew. The Hebrew word for "month", chodesh, is derived from the word for "new", chadesh; the implication is that the Ketubah inaugurates the couple's new life together. Pre-printed Ketubahs are available commercially, though many couples have their Ketubahs hand-calligraphed. A great deal of creativity and personalization can go into the illumination, making the Ketubah more than a dry utilitarian contract, turning it into a beautiful and meaningful work of art.
Sources: A Jewish Wedding http://dcubed.com/ajw/one.html
The Ketubah http://www.theketubah.com/
Ketubah by Karny http://www.ketubahbykarny.com/