Rosh Hashanah, which literally means the head of the year, commemorates the anniversary of the creation of the world. It is celebrated on the first and second days of the seventh Hebrew month, Tishri.

Rosh Hashanah, when all living things are judged, is often referred to as the beginning of the Jewish New Year. However, the Hebrew month of Nissan, in which Passover is celebrated, is, really, the first month of the Jewish calendar. Rosh Hashanah is actually only one of four symbolic Jewish new year celebrations. The commandment to observe Rosh Hashanah is found in the second and third books of the Torah.

In the seventh month, in the first day of the month, shall be a solemn rest unto you, a memorial proclaimed with the blast of horns, a holy convocation... and you shall bring an offering made by fire unto the Lord. Leviticus 23:24-5

In the seventh month, on the first day of the month, you shall observe a holy day; you shall not work at your occupations. You shall observe it as a day when the shofar is trumpeted. Numbers 29:1

The first two days of Tishrei were not called Rosh Hashanah until Talmudic times. Jewish leaders of the day may have been reluctant to promote large celebrations around a fall new year because moon festivals were common among pagan religions. Many Near Eastern religions, for example, celebrated divine coronation festivals in the Fall.

By the fourth century, B.C.E., when the Jews returned from Babylonian exile to build the second temple, Rosh Hashanah was well established. By the time of the Mishnah, the codification of Jewish oral tradition, Rosh Hashanah had developed a more serious tone. Now, having suffered the loss of the second temple, Rosh Hashanah emphasized the anniversary of creation, and of G-d as judge, dispensing mercy or justice to those who do or do not repent their sins.

The Torah refers to Rosh Hashanah as Yom Teruah, the day of sounding the shofar, the traditional ram's horn. It is also called Yom Ha'Din, the day of judgment as well as Yom Hazikaron, the day of remembering. These are the terms used in the Mahzor for the holidays, as well. Yom Hazikaron is a reference to the patriarch Abraham who offered his only son, Isaac, to G-d as proof of his obedience. As the result of his readiness to sacrifice Isaac, G-d caused a ram to appear and be killed instead.