The Amidah (Hebrew: תפילת העמידה, Tefilat HaAmidah, 'The Standing Prayer'), also called the Shemoneh Esreh (שמנה עשרה 'eighteen'), is the central prayer of the Jewish liturgy. Observant Jews recite the Amidah at each of three daily prayer services in a typical weekday: morning (Shacharit), afternoon (Mincha), and evening (Ma'ariv). On Shabbat, Rosh Chodesh, and Jewish festivals, a fourth Amidah (Mussaf) is recited after the morning Torah reading, and once per year a fifth Amidah (Ne'ilah) is recited, around sunset on Yom Kippur. Due to the importance of the Amidah, in rabbinic literature it is simply called "hatefila" (התפילה, "the prayer"). According to legend, the prayer was composed by the Rabbis of the Anshei Knesset HaGedolah (c. 515-332 BCE). Accordingly, in Judaism, to recite the Amidah is a mitzvah de-rabbanan, i.e., a commandment of rabbinic origin.

Although the name Shemoneh Esreh ("eighteen") refers to the original number of component blessings in the prayer, the typical weekday Amidah actually consists of nineteen blessings.

Among other prayers, the Amidah can be found in the siddur, the traditional Jewish prayer book. The prayer is recited standing with feet firmly together, and preferably while facing Jerusalem. In Orthodox public worship, the Amidah is usually first prayed quietly by the congregation and is then repeated aloud by the chazzan (reader); it is not repeated in the Maariv prayer. 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 of Orach Chaim. 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 (usually just one) specific to the occasion.