The Shabbat before Rosh Hodesh is called Shabbat Mevarkhim, the “Shabbat of Blessing of the Month,” because of the prayer that is recited in the synagogue on that occasion. This “Blessing of the Month” consists of a proclamation of the day or days of the upcoming week upon which Rosh Hodesh will fall, together with a prayer that the new month will be one of material and spiritual blessing.

The Blessing of the Month is recited after the reading of the Torah, before the Musaf prayer service. The congregation stands and recites the text of the blessing for the approaching month, and the exact day or days that will be Rosh Hodesh are announced. Before proclaiming the days of Rosh Hodesh, it is proper to be aware of the precise time of the “birth” [molad] of the moon, the moment when it becomes visible again after having disappeared from view. This represents the beginning of the new lunar cycle. In many communities it is customary to announce the time of the molad before announcing the days of Rosh Hodesh. The prayer leader [hazan] holds a Torah scroll during the Blessing of the Month.

Some observe special customs on this Shabbat that are not observed on a regular Shabbat. Lubavitch Hasidim have the custom to rise early in the morning so that the entire congregation can recite together the whole book of Psalms.

On a Shabbat when Rosh Hodesh will fall on the following day (Sunday), a special haftara (reading from the Prophets) is recited, from I Samuel 20:18–42, whose opening verse contains the phrase: “Tomorrow is the new moon.”