The sounding of the shofar is the central commandment on Rosh HaShana, and for this reason it is called by the Torah “the day of shofar blasts” [yom terua]. Rav Se’adya Gaon listed ten rationales for this mitzva. Among them are the following:

On this day we reaccept upon ourselves the kingship of God, and it is customary to blow trumpets to herald the arrival of a king.

The shofar awakens people’s hearts to repentance, as the prophet Amos says: “Will the shofar be sounded in a city, and the people not tremble?” (Amos 3:6).

The ram’s horn recalls before God the ram that Abraham sacrificed in place of his son Isaac.

The sound of the shofar evokes in our hearts the memory of the giving of the Torah at Mount Sinai, when the people heard “the blast of a shofar extremely powerful” (Exodus 19:16).

The commandment of the shofar is a time-bound positive mitzva, and as such, women are exempt from it. Nevertheless, many women have taken upon themselves to observe this mitzva, and therefore they too should hear the shofar; they may even recite the blessing over the shofar blowing when the shofar is being sounded for them alone. It is also recommended to bring one’s children to the synagogue to hear the shofar as well, in order to educate them in the performance of mitzvot, provided that they will not disturb the congregation.

This mitzva can be fulfilled at any time throughout the day. Accordingly, if someone missed hearing the blasts in the synagogue, he should blow the shofar himself, or find someone who can do so for him, at any point before sunset.

After the reading of the Torah and the haftara, the congregation prepares itself for the sounding of the shofar, which is the climax of Rosh HaShana. The sounding of the shofar is performed on both days of the festival, except when the first day of Rosh HaShana falls on Shabbat, in which case the shofar is not sounded. Instead, the prayers continue directly with Musaf, and the shofar is sounded only on the second day of the festival.

The shofar can be made of the hollow horn of any kosher animal, as long as it is naturally hollow, as opposed to a unified mass that must be chiseled out. However, the horn of a cow may not be used. There is a halakhic preference for a shofar made from the horn of a ram, and it is a ram’s horn that is used for the mitzva in almost all communities. In some Yemenite communities they use an elongated, twisted shofar, which is made from a horn of a kudu (an African antelope).

The mitzva of shofar on Rosh HaShana entails blowing or hearing a series of thirty blasts, consisting of three types of sound called tekia, shevarim, and terua. The tekia is one long blast; shevarim consists of three medium-length sounds; and terua is a series of at least nine short sounds.

By Torah law, one is obligated to hear only nine shofar blasts: three sets of tekia-terua-tekia. If so, how did we get to thirty? The requirement to blow thirty blasts evolved from a discussion among the Sages in the Talmud over the exact definition of the terua required by the Torah. Is it a sound that is reminiscent of moaning (that which we call shevarim), or whimpering (that which we call terua)? Or is it perhaps a combination of both (that which we call shevarim-terua)? Since the question was not decisively settled, the talmudic Sage Rabbi Abbahu instituted the series of blasts that is customarily performed today, which combines all the possibilities:

First a series is sounded that accounts for the possibility that the terua required by the Torah is a combination of the blasts currently known as shevarim and terua. Therefore, the series of tekia-shevarim-terua-tekia (sometimes referred to as “tashrat,” which is an acronym of the words tekia, shevarim, terua, and tekia) is blown three times.

After this set, blasts are sounded that conform with the other two possibilities, that perhaps the terua referred to in the Torah is what is currently referred to as a shevarim, or what is currently referred to as a terua. Consequently, three sets of tekia-shevarim-tekia (sometimes called “tashat”) are sounded, followed by three sets of tekia-terua-tekia (sometimes called “tarat”).

This sequence of blasts, which includes all the possibilities, consists of a total of thirty sounds, and this is the basic obligation of the mitzva of shofar on Rosh HaShana.

Although one has certainly fulfilled the mitzva upon hearing thirty blasts, it is customary to blow one hundred blasts in the synagogue on the morning of Rosh HaShana. Thirty blasts are blown before the beginning of Musaf, the additional prayer service. During the cantor’s repetition of the Amida of Musaf, an additional thirty blasts are blown, and then during Kaddish after the cantor’s repetition an additional forty blasts are sounded, bringing the total to one hundred. In Sephardic and hasidic communities, besides the thirty blasts blown before Musaf, it is customary to sound thirty blasts during the silent Amida of Musaf, thirty more during the cantor’s repetition, and only ten during Kaddish following the cantor’s repetition.

The person sounding the shofar, who is called the ba’al toke’a, should be a God-fearing man who is meticulous in his mitzva observance. It is preferable for him to be married, over the age of thirty, a father, and not involved in any conflict with any member of the congregation. Another man stands alongside the ba’al toke’a to call out the name of the upcoming sound, so as to avoid confusion in the sequence of the blasts.

Before the blasts it is customary to recite Psalms 47 seven times, and then to say a series of verses whose initial letters form the words kera Satan, meaning “hinder [literally, “tear”] Satan.” This is an appeal to God to deter the accusations of the accusing angel against the Jewish people.

Before the blasts, the ba’al toke’a recites two blessings aloud:

“Blessed are You, Lord our God, King of the universe, who sanctified us through His commandments, and commanded us to hear the sound of the shofar.”

“Blessed are You, Lord our God, King of the universe, who has given us life, sustained us, and brought us to this time.”

The congregation answers “amen” after each of the blessings, with the intention of fulfilling their obligation concerning both the recitation of the blessings and the blasts themselves. The ba’al toke’a should also have in mind that he is reciting the blessings and blowing the shofar on behalf of the entire congregation.

After the blessings, the ba’al toke’a sounds the first thirty blasts. They are called “the blasts heard while sitting,” as in principle the congregation may listen to them when they are seated. Nevertheless, in most communities it is customary to stand for all the blasts. After these blasts, the congregation recites a few more verses and then the Musaf service begins.