Rabbi El'azar Berabbi Qillir (commonly known as "HaQallir") was the most famous and productive of the Hebrew poets during the peak era of early Hebrew piyyut (liturgical poetry) between the sixth and eighth centuries AD. Of the thousands of poems he penned, some were preserved in the Asheknazi, French and Italian mahzorim (prayer books) for the High Holy Days, and a few of them are recited in synagogues to this day. Notable examples of such from among his Yom Kippur poems are the poems "Praise God: Almighty, King of His universe" ("אמרו לאלהים: אל מלך בעולמו") and "The work of our God! He is mighty amidst His [Divine] assembly" ("מעשה אלהינו אדיר בוויעודו"); these two poems are still recited even in those Ashkenazi communities which skip most of the other poetic segments recorded in the mahzorim for the High Holy Days. The Cairo Geniza findings indicate that the European mahzorim preserve only a handful of Qillir's works for Yom Kippur. In fact, he adorned each of the day's prayers with several poetic compositions, most especially with qedushta'ot, arrays of poems intended to be recited as part of the amidah ("the standing prayer"), anticipating the recitation of the qedusha. Time and again, Qillir penned new compositions intended to replace the previous ones. Alongside his qedushta'ot for musaf and for ne'ila which are found in the Ashkenazi mahzorim, the Genizah fragments reveal additional Qillirian qedushta'ot for these same prayers, as well as poems for ma'ariv, shaharit and minha. In addition, it turns out that the qedushta'ot in the Asheknazi mahzorim were corrupted; some of the original Qillirian segments were omitted, and later non-Qillirian segments were interpolated at various places. The present edition comprises a collection of all of the surviving poems authored by Rabbi El'azar BeRabbi Qillir for all of the Yom Kippur prayers. This edition attempts to restore the full compositions as per the textual witnesses from the Cairo Genizah, with the aid of the material from the European mahzorim. The poems are printed with full vocalization, apparatus criticus, and extensive running commentary. The restoration of the qedushta'ot incurred many questions, discussed in detail in the introduction. The introduction includes a comprehensive exploration of the multiple segments contained in each of Qillir’s compositions, including a discussion of the exact purpose of each segment and a justification of its attribution to Qillir. The introduction also describes the prosodic structures of Qillir’s poems for Yom Kippur, their poetic characteristics, their unique language and stylistics, and their thematic content. An additional section focuses upon rare midrashic traditions reflected within the poems, as well as rare Jewish legal traditions and customs. Many of the poetic segments contained herein have never before appeared in a proper scientific edition, including spectacular works such as silluq (the segment immediately prior to the qedusha) for musaf; a series of rahitim (poems prior to the silluq) expounding upon the verses describing the High Priest's work on Yom Kippur, and another series of over twenty rahitim praising God, which are without a doubt among Rabbi El'azar BeRabbi Qillir's finest works; and sidre pesukim (poetic compositions which expound upon the Biblical verses which were recited during that era within the amidah itself). In his compositions for the minha prayer, Qillir often dedicates the rahitim to the story of Elijah the Prophet on Mount Carmel; several of these describe the miracle of the fire coming down from the sky, and primarily Elijah's prayer – which in effect becomes the poet's prayer for his audience. Perusal of the poems reveals quite a few surprises, from original linguistic feats to previously unknown Midrash traditions, and above all, uplifting segments of poetry. Several of these are presented in the introduction, but the edition is the crux of the book, and through it readers will be able to delve deep into Qillir's Yom Kippur poems, to learn from the Torah contained within them, and to delight in their beauty.