This article explores trends and motivations in the selection of plainchant and vernacular song quotations as the foundations of thirteenth-century motets. I argue that particular tenor melodies that received only cursory treatment in the liturgical polyphony of the Magnus liber organi were adopted in motets on account of their brevity and simplicity, characteristics that enabled their combination with upper-voice song forms and refrain quotations. Demonstrating a preference for short and simple tenors within the earliest layers of the motet repertoire, I trace the polyphonic heritage of the tenor omnes, whose simple melody enabled its combination with another more obscure plainchant quotation, aptatur, in a unique double tenor motet. I propose that motet creators—while sensitive to the semantic connotations of tenor texts—exploited the musical ability of tenor quotations to be combined with or stand in for other musical quotations. Newly identifying a plainchant tenor source in a motet by Adam de la Halle, I show that Adam's polyphonic motet quotations of his own three-voice polyphonic rondeaux were achieved by the careful selection of motet tenors to replicate the freely conceived lowest voices of these preexisting rondeaux. The article further reveals profound modal and melodic similarities between the quotations chosen as thirteenth-century motet tenors and the newly composed lowest voices of polyphonic rondeaux and English pes motets. It offers new perspectives on the relationship between the “elite” genre of the motet and types of polyphony that are less well attested in written sources, often considered to inhabit a more “popular” realm of musical practice.