The correct way to set the mezuzah on your door post (or these days on your car post and computer screen) is to angle the upper part of the rolled-up scroll closer to the inside of the room, about one third way down at a reachable height for the adult residents. Why?

We are told twice in the Deuteronomy 6:9, 11:20 to "write on the doorposts of your house" but no directions for angle, casing or orientation are given. So where does the tradition come from to angle a mezuzah?

In the Talmud, a compendium of early Jewish laws, stories and customs, the sage Yehudah quotes a saying of a first generation Babylonian Jewish scholar, an amora, who lived approximately 225 C.E.: "If it is fixed in the manner of a bolt, it is invalid."  Now, whatever did that mean? Around the year 1040 the medieval commentator Rashi declares the manner of a bolt to be horizontal. By the 12th Century Rabbenu Tam says this same phrase means vertically.  Just think how much hardware has changed in our times, we'd have trouble agreeing on the meaning too!

The next important stop in our investigation is the Shulchan Arukh, the sixteenth century law code Yoreh De'ah (289:6) where R' Joseph Caro asserts that a mezuzah "must be vertical, its length must be parallel to the opening edge of the doorpost." So you could say that Rashi prevailed, at least in Sephardic communities where R'Caro was a formal authority for Jewish law.

An Ashkenazic leader, R'Isserles reviewed this code in its time and felt the Sephardic opinion to be so different to the norms in his region that he added his own note: "there are those who say a vertical mezuzah is invalid, that it must be oriented horizontally, with its length parallel to the top of the door."  He continued on by saying that some fulfill both views by "putting the mezuzah on a slant, diagonal and so we do in these countries, with the Sh'ma angled inside and the bottom edge of the parchment toward the outside."

Jews from eastern Europe have followed the diagonal ever since. Sephardic Jews vary in practice, the former Sephardic Chief Rabbi of Israel, R'Ovadia Yosef taught to place the mezuzzah vertically as did R'Chaim David ha-Levi, the former Chief Rabbi of Tel Aviv, although he also wrote permitting the slanting method.

What flavor will you choose when hanging your mezuzah? If there's not enough space to angle it, by the way, it will end up vertical no matter what! But IMHO, it's the intentionality behind the action that matters most, so click here to view a guide to holding a hanukkat ha bayit, a house dedication by means of a mezuzah hanging party!