The Ashrei (Hebrew: אַשְׁרֵי יוֹשְׁבֵי בֵיתֶךָ, עוֹד יְהַלְלוּךָ סֶּלָה, Ashrei yoshvei veitecha, od y’hallelucha, selah!; English: Happy are they who dwell in Your house; they will praise You, always!) is a prayer that is recited at least three times daily in Jewish prayers, twice during Shacharit (morning service) and once during Mincha (afternoon service). The prayer is composed primarily of Psalm 145 in its entirety, with a verse each from Psalms 84 and 144 added to the beginning, and a verse from Psalm 115 added to the end. The first two verses that are added both start with the Hebrew word "ashrei" (translating to "happy" or "praiseworthy" or "fortunate"), hence the prayer's name.
Ashrei is recited three times daily during the full course of Jewish prayers, in accordance with the Talmud, citing Rabbi Eleazar ben Abina of the 4th century, which says that one who thoughtfully recites Ashrei three times daily, particularly the verse פותח ("Thou openest thine hand, and satisfiest the desire of every living thing"), is guaranteed a place in Olam Haba (the World to Come). It is for this reason that not only is Ashrei recited these three times, but many of its verses occur throughout liturgy.
Ashrei is recited twice during Shacharit (once during Pesukei D'Zimrah and once between Tachanun/Torah reading and Psalm 20/Uva Letzion or in this place when any of these are omitted), and once as the introduction to Mincha; it is also recited at the commencement of Selichot services, on Yom Kippur, Ashkenazim recite it during Ne'ila instead of during Mincha, Sefardim recite it during both Mincha and Ne'ila. Such is the practice of the Ashkenaz, Sefardic, and Mizrahi; but the Romaniot and Rome traditions have it only on Mondays and Thursdays, and on holy days on which Supplications are not recited.