In countries with parliamentary systems, the head of state is typically a ceremonial figurehead that does not actually guide day-to-day government activities or is not empowered to exercise any kind of secular political authority (e.g., Queen Elizabeth II of the Commonwealth Realms). In countries where the head of state is also the head of government, the head of state serves as both a public figurehead and the actual highest-ranking political leader who oversees the executive branch (e.g., the President of Brazil).
An independent nation state normally has a head of state, and determines the extent of its head's executive powers of government or formal representational functions. In protocolary terms, the head of a sovereign, independent state is usually identified as the person who, according to that state's constitution, is the reigning monarch, in the case of a monarchy, or the president, in the case of a republic.
Among the different state constitutions (fundamental laws) that establish different political systems, four major types of heads of state can be distinguished: