Medieval historian al-Tabari (c. 828-923 CE) was a brilliant scholar of 'Abbasid Baghdad who wrote extensively in all fields of the Islamic science of his day: historiography, scriptural interpretation and jurisprudence. His massive History of the Messengers and Kings is the primary source for the information that we have about Sasanian Persia and the first three centuries of Islam. As well as being a historical record of outstanding importance, it is also of the greatest interest for what is says about the principles of good Islamic governance. In a concise overview of his life, thought and major writings, Ulrika Mårtensson explores the philosophy and methodology than underpin Tabari's thinking, and places his work in the context of the complex - and sometimes administratively heterogeneous - society that comprised the 'Abbasid Caliphate. Tabari's argument that effective government is dependent on merit, not preferment, and on the separation of political and religious authority, is shown to have much contemporary resonance for Muslims.