A mezuzah (Hebrew: מזוזה "doorpost") is a parchment scroll, handwritten by a qualified scribe and placed in a decorative case fixed to the front right doorpost (and usually to all rooms) of a Jewish home. The scroll is inscribed with the first two portions of the Shema Israel, consisting of Deuteronomy 6:4-9 and Deuteronomy 11:13-21. The practice is is in obedience to the first passage quoted, which ends: "And you shall write them on the doorposts of your house and on your gates." On the back of the scroll, a name of God is written. The scroll is then rolled so that the first letter of the Name (the letter Shin) is visible (or, more commonly, the letter Shin is written on the on the upper exterior of the case). The case is attached slanting upwards towards the door. Every time you pass through a door with a mezuzah on it, you kiss your fingers and touch them to the mezuzah, expressing love and respect for God and his commandments.
The mezuzah represents the inseparable link between prayer and study of the Torah and the dual importance of home and synagogue for observance of the mitzvot. The Mezuzah is not a good-luck charm, nor does it have any connection with the lamb's blood placed on the doorposts in Egypt.