Originally, the date of Rosh Chodesh was confirmed on the testimony of witnesses observing the new moon, a procedure known as kiddush hachodesh (sanctification of the month).

[6] After the Sanhedrin declared Rosh Chodesh for either a full (30-day) or defective (29-day) month, news of it would then be communicated throughout Israel and the diaspora.

Some communities customarily precede the prayer by an announcement of the exact date and time of the new moon, referred to as the molad, or "birth".

An additional prayer service, called Mussaf, is added to commemorate the Rosh Chodesh sacrifices in the Temple.

The central benediction is replaced with an alternative version (Ata Yatzarta) that mentions both the Shabbat and Rosh Chodesh.

Kiddush Levanah is recited soon after Rosh Chodesh, although most communities wait until three or seven days after the Molad (the time of the "birth" of the new moon).

Jews nowadays generally treat Rosh Chodesh as barely different from any other weekday (except for expansion of the prayer service).

[15] The Jerusalem Talmud states that women refrain from work on Rosh Hodesh, but only by custom as opposed to law.

In some Biblical sources, Rosh Hodesh is described as a day when business is not conducted[18] and which seems to have been devoted to worship[19] and feasting.

[26] Rashi, in commenting on this passage, delineates the activities from which they must refrain: spinning, weaving, and sewing—the skills that women contributed to the building of the Mishkan (Tabernacle).

[17] The midrash Pirke De-Rabbi Eliezer gives a historical explanation for this practice: Aaron argued with himself, saying: "If I say to Israel, 'Give ye to me gold and silver,' they will bring it immediately; but behold I will say to them, 'Give ye to me the earrings of your wives and of your sons,' and forthwith the matter will fail," as it is said, "And Aaron said to them, 'Break off the golden rings.'"

Many Rosh Chodesh groups explore spirituality, religious education, ritual, health issues, music, chanting, art, and/or cooking.