The following description was prepared by William Gross:
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 compose the Jewish prayer "Shema Yisrael", beginning with the phrase: "Hear, O Israel, the LORD (is) our God, the LORD is One". In mainstream, i.e. Rabbinic Judaism, a mezuzah is affixed to the doorframe of 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 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.
The Mezuzot used for the doorpost of the frontdoor, remaining outside, were by and large of very simple materials, either simply carved wood or plain painted tin. Only in the twentieth century did outside Mezuzot of quality begin slowly to be made available. This is one of the early examples, a cast Mezusah from Poland, with its parchment still inside.