The nature of the psalms was heatedly debated by Rabbinites and Karaites. Both viewed psalms as prophetic. Both included psalms in their liturgies. But they differed in whether the psalms were central or ancillary to a prayer service, in how psalms might be used in personal prayer, and in what ways psalms might legitimately be interpreted. The debate was outlined by Uriel Simon in Four Approaches to the Book of Psalms. In this talk, I extend Simon`s work by analyzing the impact of the debate on two bodies of texts: the traditional siddur and commentary on individual psalms. First, the debate influenced the selection and placement of psalms in the siddur. The Karaites made all 150 psalms available for entreating God to solve daily problems as well as for rescue from exile. In contrast, the Rabbanite siddur includes only 54 psalms, mainly hymns and communal thanksgivings, and treated them as ancillary rather than as real prayer. I argue that the siddur omits first-person laments because these are most prayer-like. Second, while Simon focused on the introduction sections to Rabbinite and Karaite translations and commentaries on the Book of Psalms, I study comments on exactly those psalms that present the biggest challenges to the Rabbintes. In this talk, I will show that Rabbinite interpretations of these psalms—for example limiting interpretations of Psalm 22 to Esther or King David, are designed to shut down the option for Jews to use them as personal prayer.