Head of state

A head of state (or chief of state) is the public persona that officially represents the national unity and legitimacy of a sovereign state. In some countries, the head of state is a ceremonial figurehead with limited or no executive power, while in others, the head of state is also the head of government.

In countries with parliamentary governments, the head of state is typically a ceremonial figurehead that does not actually guide day-to-day government activities and may not be empowered to exercise any kind of secular political authority (e.g., Queen Elizabeth II as Head of the Commonwealth). In countries where the head of state is also the head of government, the president serves as both a public figurehead and the actual highest ranking political leader who oversees the executive branch (e.g., thePresident of the United States).

Constitutional models
Some academic writers discuss states and governments in terms of "models".

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:
 * 1) The parliamentary system, with two subset models;
 * 2) The standard model, in which the head of state, in theory, possesses key executive powers, but the exercise of such power is done on the binding advice of a head of government (e.g., United Kingdom, India, Pakistan).
 * 3) The non-executive model, in which the head of state has either none or very limited executive powers, and mainly has a ceremonial and symbolic role (e.g., Sweden, Japan).
 * 4) The semi-presidential system, in which the head of state shares key executive powers with a head of government or cabinet (e.g., Russia,France, Sri Lanka); and
 * 5) The presidential system, in which the head of state is also the head of government and has all executive powers (e.g., United States,Indonesia).