The survival of a large number of twelfth- through fifteenth-century copies of canon law texts testifies to their great utility to contemporaneous masters and students, lawyers and judges, and ecclesiastics of varying ranks and occupations. In modern times these handwritten witnesses to the generation, study, and application of canon law continue to be carefully studied for their texts and accompanying notes, explanations, and glosses, written between the lines or in the margins of the page. Through comparison of divergent commentaries and the tabulation of variant editions of the texts, scholars have been able to trace the chronological development of judicial thought and practice. But this is not the whole story. While there is relatively little documentary evidence about the manner in which early classes of law were organized and taught before the institutionalization of learning in universities, the manuscript pages provide valuable evidence of input to and interaction with the text by master and student. Queries and elucidations transcribed in the margins of early canon law manuscripts, along with indications of cross-references in the same text, embody problems raised and discussed during lectures. Further graphic and pictorial signs mark material to be memorized or utilized in classroom debates.