By the end of the Umayyad period, the government bureaucracy, organized as a group of dīwāns or government departments concerned with finance, official correspondence and the mustering and payment of the army, was already well formed. Under the ʿAbbasids, the existing dīwāns increased in size and complexity and were complemented by new ones with more specialized functions, such as confiscations (the dīwān al-muṣādarāt) and financial control and accounting (the dīwān al-zimām wa-ʾl-istīfāʾ). The role of the secretaries (kuttāb, sing, kātib), whose function had been of comparatively low standing under the Umayyads, now grew, possibly stimulated by the importance of the personal secretary to the last Umayyad caliph Marwān II (reigned 127–32/744–50), ʿAbd al-Ḥamīd b. Yaḥyā. This kātib class acquired a prestige in the ʿAbbasid state similar to that of its pre-Islamic predecessors in Persia and Iraq, the Sasanid dibhērān, whilst the coming to full form of the office of vizier or chief executive for the caliph, achieved under the originally eastern Iranian Barmakī family in the second half of the second/eighth century, allowed the secretaries to aspire to the highest position in the state beneath the ruler himself, and to give the central administration a distinct bias towards long-established Persian traditions of statecraft.

Despite this increased administrative proliferation and complexity, the positions of the exchequer, dealing with finance and taxation, and of the chancery, dealing with correspondence, remained pre-eminent.