Literature documenting legal disagreement and dissent (fiqh al-khilaf or ikhtilaf) stands at the juncture between the theoretical jurisprudence of Islamic legal theory (usul al-fiqh) and the practical application of positive law (furu‘). Khilaf literature first appeared as a distinct genre in the 4th/10th century. To date there has been no sustained analysis of the historical emergence of this genre and how its evolution was shaped by contemporaneous developments in usul al-fiqh and furu‘. Some of the questions that are yet to be explored include: Was the development of khilāf anticipated in literature written prior to the 4th/10th century? What was the earliest theorization of legal disagreement and its relationship to positive law? What was the purpose and use of the earliest khilaf works? Why did works of legal disagreement emerge in the particular time and place that they did? To begin addressing these questions, I provide a survey of four khilaf works from the 3rd-4th/9th-10th centuries: Abu ‘AbdAllah al-Marwazi’s (d. 294/906)’s Ikhtilaf al-’Ulama’, Muhammad b. Jarir al-Tabari’s (d. 310/923)’s Ikhtilaf al-Fuqaha’, Ibn al-Mundhir (d. 318/930)’s Al-Sunan al-Awsat and Abu Ja‘far al-Tahawi’s (d. 321/933) Ikhtilaf al-Fuqaha’. My analysis focuses primarily on the chapter of the nullifiers of ablution (nawaqid al-wudu') because it contains several issues that are fairly contentious yet accessible; disagreements that have spawned extensive commentary with involved theoretical arguments and counter-arguments. My analysis of this chapter substantiates the following provisional conclusions about khilaf works: (1) In the earliest legal writings we find a recognition of the uncertain and probabilistic nature of the law, which in turn validated the complex of mutually contradictory legal positions posited by jurists; (2) Works compiling legal disagreements most often act as a systematic justification for the madhhab of their respective authors; (3) The causes of juristic disagreement are not always clear in early khilaf works, and where they are discussed, it is often in a cursory and indirect fashion. This seems to indicate that khilaf works presupposed a familiarity with the divergent approaches of legal theory, theorized in usul al-fiqh literature; (4) Finally, the way in which later scholars held up legal disagreements seems to indicate a remarkable continuity between formative and post-formative legal reasoning.