The Amidah (Hebrew: תפילת העמידהTefilat HaAmidah  "The Standing Prayer"), also called the Shmoneh Esreh (שמנה עשרהShmoneh Esreh "The Eighteen," in reference to the original number of constituent blessings; there are now nineteen), is the central prayer of the Jewish liturgy. This prayer, among others, is found in the siddur, the traditional Jewish prayer book. As Judaism's central prayer, the Amidah is often designated simply astefila (תפילה, "prayer") in Rabbinic literature.

Observant Jews recite the Amidah at each of three prayer services in a typical weekday: morning, afternoon, and evening. A special abbreviated Amidah is also the core of the  Mussaf  ("Additional") service that is recited on Shabbat (the Jewish Sabbath), Rosh Chodesh (the day of the New Moon), and Jewish festivals, after the morning Torah reading, with various forms of the Amidah that depend on the occasion. The typical weekday Amidah actually consists of nineteen blessings, though it originally had eighteen; when the Amidah is modified for specific prayers or occasions, the first three blessings and the last three remain constant, framing the Amidah used in each service, while the middle thirteen blessings are replaced by blessings specific to the occasion.

The language of the Amidah most likely dates from the mishnaic period, both before and after the destruction of the Temple (70 CE) at which time it was considered unnecessary to prescribe its text and content.[1] The Talmud indicates that when Rabbi Gamaliel II undertook to fix definitely the public service and to regulate private devotion, he directed Samuel ha-Katan to write another paragraph inveighing against informers and heretics, which was inserted as the twelfth prayer in modern sequence, making the number of blessings nineteen.[2] Other sources, also in the Talmud, indicate, however, that this prayer was part of the original 18;[3] and that 19 prayers came about when the 15th prayer for the restoration of Jerusalem and of the throne of David (coming of the Messiah) was split into two.[4]

The prayer is recited standing with feet firmly together, and preferably while facing Jerusalem. In Orthodox public worship, the Shemoneh Esrei is usually first prayed silently by the congregation and is then repeated aloud by the  chazzan  (reader); the repetition's original purpose was to give illiterate members of the congregation a chance to participate in the collective prayer by answering "Amen." Conservative and Reform congregations sometimes abbreviate the public recitation of the Amidah according to their customs. The rules governing the composition and recital of the Amidah are discussed primarily in the Talmud, in Chapters 4–5 of Berakhot; in the Mishneh Torah, in chapters 4–5 of  Hilkhot Tefilah ; and in the Shulchan Aruch, Laws 89–127.

Service Section: Amidah 
Source: Wikipedia