What is a Mezuzah?

The mezuzah is affixed to the right side of the doorpost when entering a room about one-third of the way down from the top of the doorpost.For Ashkenazi Jews, it is traditionally positioned at a slight angle, with the top pointing toward the inside of the house or room. This angle is a compromise between different rabbinic opinions on whether it should be vertical or horizontal. (So many opinions!) Sephardic Jews tend to have the mezuzah be vertical.

Which doors need a mezuzah?

Where do we hang a mezuzah? All living spaces in a Jewish home require a mezuzah, except for bathrooms and very small rooms. The main entrance is the most important place for a mezuzah so many people at least have one there. Businesses and offices owned by Jewish people often have a mezuzah as well. You may have seen one at a kosher restaurant!

What is the blessing when placing a mezuzah on the door?

Before affixing a mezuzah, a special blessing (berachah) is recited:
"Baruch atah Adonai, Eloheinu Melech ha’olam, asher kiddeshanu b’mitzvotav v’tzivanu likbo’a mezuzah."
(Blessed are You, Lord our God, King of the Universe, who has sanctified us with His commandments and commanded us to affix a mezuzah.)

Other notes

Many observant Jews touch the mezuzah with their hand and then kiss their fingers when passing by. This is a sign of respect and a reminder of God’s presence.

The letters can fade over time, so Jewish law requires that mezuzahs be checked twice every seven years (some check them annually).