This paper investigates the relationship between medieval Islamic empires and the large classes of merchants that provided them with tax revenue and other essential services. Looking particularly from the angle of taxation on transit trade and individual merchant-amīr relationships, the main question it asks is: were merchants using the state as an apparatus to further their interests and needs or were state officials getting involved in trade in order to keep the merchants in check and impose state interventions? In more general terms, what did it mean for the state to be involved in commercial activities and how did that inform state governance and policies directly and indirectly? Scholars of medieval Europe have shown how states were often instruments for mercantile interests and that state power was partly wielded through commercial activities. In the Islamic context, scholars have long believed that there was not enough surviving evidence to evaluate whether a similar connection existed between Islamic polities and merchant classes. Surviving narrative sources, such as chronicles, are generally silent on this topic. The documentary evidence preserved in the Cairo Geniza includes scores of merchant letters from the eleventh and twelfth centuries CE in Judaeo-Arabic and Arabic, as well as state and legal documents that shed light on this issue and inform our understanding of how commercial activities took place in Medieval Islamic Empires. Merchant letters frequently mention requisitions by Fatimid amīrs (state officials) as well as the role of state-owned ships in delivering commodities arriving on state-owned ships and the activities of merchants selling goods on behalf of amīrs. This paper uses Geniza documents to overcome the silence of the narrative sources and to debunk the idea that insufficient sources for this economic history have survived. My findings demonstrate how the merchants used the state to further their economic interests and how the state simultaneously sought to control merchant activities for their own strategic needs and by imposing taxes on every step of trade and production.