Мезуза: Свиток в декоративном футляре.

Piece of parchment in a decorative case

A mezuzah ( "doorpost"; plural: מְזוּזוֹת mezuzot) is a piece of parchment inscribed with specific Hebrew verses from the Torah, which Jewish followers of Rabbinical Judaism fix to the doorposts of their homes. These verses are the Biblical passages in which the use of a mezuzah is commanded (Deuteronomy 6:4–9 (HE) and ); they also form part of the Shema prayer. In mainstream Rabbinic Judaism, a mezuzah must generally be placed in every doorway in the home, with some exceptions such as bathrooms (which are not a living space) and small closets. The klaf is prepared by a qualified scribe ("sofer stam) who has undergone training, both in studying the relevant religious laws, and in the more practical parts, i. e. carving the quill and practising writing. The verses are written in black indelible ink with a special quill pen made either from a feather or, now quite rare, a reed. The klaf is then rolled up and placed inside the case.

While the most important part of the mezuzah is the klaf, or the parchment, and not the case itself, designing and producing mezuzah cases has been elevated to an art form over the ages. Mezuzah cases are produced from a wide variety of materials, from silver and precious metals, to wood, stone, ceramics, pewter, and even polymer clay. Some dealers of mezuzah cases will provide or offer for sale a copy of the text that has been photocopied onto paper; this is not a kosher (valid) mezuzah, which must be handwritten onto a piece of parchment by a qualified scribe.

According to halakha, the mezuzah should be placed on the right side of the door or doorpost, in the upper third of the doorpost (i. e., approximately shoulder height), within approximately of the doorway opening. Care should be taken to not tear or damage the parchment or the wording on it, as this will invalidate the mezuzah, which is considered Torah.

Where the doorway is wide enough, many Ashkenazi Jews tilt the mezuzah so that the top slants toward the room into which the door opens. This is done to accommodate the variant opinions of Rashi (1040–1105) and of his grandson, Rabbeinu Tam, as to whether it should be placed vertically (Rashi) or horizontally (Rabbeinu Tam), and also to imply that God and the Torah (which the mezuzah symbolizes) are entering the room. The compromise solution was suggested by Rabbi Jacob ben Asher (c. 1269 – c. 1343). though Spanish and Portuguese Jews living in countries where the majority of Jews are Ashkenazim usually place it slanting.

Generally, halakha requires Jews living in the diaspora (i. e., outside of the Land of Israel) to affix a mezuzah within 30 days of moving into a rented house or apartment. For a purchased home or apartment in the diaspora, or a residence in Israel (owned or rented), the mezuzah is affixed immediately upon moving in. The reason for this difference is that there is an assumption that when a Jew lives in Israel, Israel shall remain their permanent residence, whereas a home in the diaspora is temporary.

Whenever passing through the doorway, many people touch a finger to the mezuzah as a way of showing respect to God. Many people also kiss their finger after touching it to the mezuzah.

Many observant Jews from all Jewish denominations have a qualified scribe check the mezuzot parchments for defects (such as small tears or faded lettering) at least twice every seven years. This job can be done by a sofer (scribe) or by anyone with similar training. A sofer also can make new mezuzot parchments which are in accordance with Jewish law.

This article deals mainly with the mezuzah as it is used in Rabbinic Judaism, but Karaite Judaism and Samaritanism have their own traditions. In Karaite Judaism the Deuteronomic verse "And you shall write them on the doorposts of your houses and your gates" is interpreted to be a metaphor and not as referring to the Rabbanite mezuzah. Thus Karaites do not traditionally use mezuzot, but put up a small plaque in the shape of the two Tablets of the Law with the Ten Commandments. In Israel, where they might try not to make other Jews feel uncomfortable, many Karaites make an exception and place a mezuzah on their doorpost as well. This can contain a blessing or a particularly holy or uplifting message. In the past they placed a stone plaque inscribed with the Ten Commandments above the house door, some examples dating back to the Byzantine (4th–7th century) and Early Muslim (7th–11th century) periods being now shown in the Israel Museum in Jerusalem. Nowadays a Samaritan mezuzah is usually made of either marble, a wooden plate, or a sheet of parchment or high quality paper, on which they inscribe select verses from the Samaritan Torah. This they place either above the house door, or inside the house, in the entrance hall or at a prominent place on a large wall. These mezuzot are found in every Samaritan household as well as in the synagogue. was rarely challenged in the United States or Canada, However, in Chicago in 2001, a condominium association at Shoreline Towers banned "mats, boots, shoes, carts or objects of any sort outside unit entrance doors", which by board vote in 2004 was interpreted to be absolute. Shoreline Towers management removed the hallway mezuzot of condominium tenants. Complaints were subsequently filed with the Chicago Commission on Human Relations, Illinois Attorney General, and U. S. Department of Housing and Urban Development, alleging housing discrimination on the basis of religion. Shoreline Towers was not the sole condominium association in Chicago with such a restriction, although one of them agreed to modify its rule. On reading a news report of the mezuzah dispute, Chicago alderman Burton Natarus drafted an amendment to the city's municipal code which made it illegal for a renter or owner of an apartment, house, or condo to be prohibited from "placing or affixing a religious sign, symbol or relic on the door, door post or entrance." Although there was opposition, it became law in Chicago that December. The first such legislation in North America, it included a maximum $500 fine for its violation. Notwithstanding this legislation, in 2006, a federal court judge determined that the rule did not violate the Federal Fair Housing Act; the district court upheld the opinion on appeal in 2008; in 2009, the U. S. Court of Appeals for the 7th Circuit in Chicago reversed the 2008 decision, and the case proceeded. Meanwhile, records of the Chicago Jewish Star were unsuccessfully subpoenaed, and Illinois' anti SLAPP legislation was applied. In 2011, a confidential settlement to the Shoreline Towers disputes was achieved. In 2006, a more narrowly focused amendment to the state's Condominium Property Act was initiated by Illinois Senator Ira Silverstein, the first such state law. In 2006, a woman in a condo building in Fort Lauderdale, Florida, was instructed to remove the mezuzah from her hallway unit and threatened with a fine. After a lengthy legal battle, the condo association was found guilty of discrimination. In 2008, House Bill 995, an amendment to the Florida Condominium Act, modeled on the Illinois state legislation, became law. In Texas in 2007, a couple living in Houston was instructed to "remove the item attached to your door frame" to avoid violating association rules. A legal battle ensued, during which a U. S. District Court judge ruled in 2008 on behalf of the condo association. Subsequently, the couple turned to Texas House of Representatives member Garnet F. Coleman. His bill to protect such religious displays, as introduced in 2009, was not adopted, but in June 2011 a slightly revised version (HB1278) was signed into law by Texas Governor Rick Perry. A bill designed to prevent mezuzah bans nationwide was proposed in 2008 (H. R. 6932) by U. S. Congressman Jerrold Nadler. It never became law.