The Introduction defines the refrain in medieval Latin song and distinguishes it from the intertextual French refrain by virtue of its necessary repetition within and across songs. Identifying the refrain as a formal feature of Latin song across genre (conductus, versus, cantilena, etc.) that inflects manuscript transmission, function, and interpretation, the Introduction also considers the historiography of the Latin refrain and refrain song, including its long-standing connection to clerical dance. The Introduction provides an overview of manuscript sources for Latin refrain songs, revealing approaches to compilation and ordering in manuscript sources that foreground the refrain. This is followed by a section on theoretical approaches to the refrain from the perspective of music and rhetoric, offering which offers a broader repertorial and cultural contextualization. The Introduction also considers questions of authorship and performance in relation to the Latin refrain song, looking to manuscript evidence and the internal evidence of the songs themselves for information on who created, copied, sang, listened to, and potentially danced to this repertoire. The Introduction concludes with outlines for Chapters 1-5.