Why did poetry and piyut disappear from the religious-Zionist High Holy Day prayer book, and what prompted their return?

This article reviews the process by which the presence of piyut - liturgical poetry - in (Ashkenazi) Religious-Zionist High Holy Day prayer books was curtailed. Piyut is examined here, in part, as a representative of non-institutionalised prayer reflecting grassroots tradition (and varying ethnic custom) as opposed to the letter of halakhic law. From this perspective, the process of decreasing the use of piyutim will be examined as the result of both the Orthodox movement and modern literary critique of piyut poetics.