The government of the Galactic Empire is not much different from its arrangement during the later years of Emperor Palpatine's reign, on paper.
It is a totalitarian regime which governs every aspect of its society, from the economy to the private life of its subjects.
The Emperor is the head of state, commander-in-chief of the military and wields supreme legislative, executive and judicial power.
The Grand Vizier, appointed by the Emperor, ensures the day to day operation and execution of Imperial law, chairing the Imperial Ruling Council; a collection of advisors, bureau directors, powerful moffs and other important members of the Imperial court. Nominally, the constitution of the council varies at the Emperor's whim - he may appoint and dismiss whoever he chooses - but the relative strength of the Emperor and the council's members dictates its operation more regularly than any rules.
The ruling council recommends measures to the Emperor. If they are enacted, it is the responsibility of Commission for the Preservation of the New Order to turn these measures into enforcible policies and condition the population to see them as desirable. The Imperial Security Bureau ensures that they are obeyed and enforced.
Beneath this centralised authority of the council, and parallel to these state agencies, the Empire is divided into administrative regions under the command of a Moff. Moffs are appointed by Imperial Decree, granting them direct, dictatorial rule of their territory, subject to Imperial law, the dictates of COMPNOR and the scrutiny of ISB.
The Moff is responsible for the good order of their territory, its productivity, loyalty and security. With such great levity in achieving these goals, Moffs compete to produce results and undertake initiatives which they believe will attract the favor of the influential and powerful or even the Emperor himself.