A mezuzah (Hebrew: מְזוּזָה‎ "doorpost"; plural: מְזוּזוֹת mezuzot) is a piece of parchment (often contained in a decorative case) inscribed with specified Hebrew verses from the Torah (Deuteronomy 6:4-9 and 11:13-21). These verses comprise the Jewish prayer "Shema Yisrael", beginning with the phrase: "Hear, O Israel, the LORD our God, the LORD is One"

A mezuzah is affixed to the doorframe in Jewish homes to fulfill the mitzvah (Biblical commandment) to inscribe the words of the Shema "on the doorposts of your house" (Deuteronomy 6:9). Some interpret Jewish law to require a mezuzah on every doorway in the home apart from bathrooms, and closets too small to qualify as rooms. The parchment is prepared by a qualified scribe (a "sofer stam") who has undergone many years of meticulous training, and the verses are written in black indelible ink with a special quill pen. The parchment is then rolled up and placed inside the case.

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 3 inches (8 cm) of the doorway opening.^{[citation needed]} 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. Generally, halakha requires that mezuzot be affixed within 30 days of moving into a rented house or apartment. This applies to Jews living in the Diaspora (i.e., outside of the Land of Israel). 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 his/her permanent residence, whereas a home in the diaspora is temporary.