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A head of government (or chief of government) is a generic term used for either the highest or second highest official in the executive branch of a
sovereign state, a
federated state, or a
self-governing colony, (commonly referred to as countries, nations or nation-states) who often presides over a
cabinet, a group of ministers or secretaries who lead executive departments. The term "head of government" is often differentiated from the term "
head of state", (e.g. as in article 7 of the
Vienna Convention on the Law of Treaties, article 1 of the
Convention on the Prevention and Punishment of Crimes against Internationally Protected Persons, including Diplomatic Agents and the United Nations protocol list),
 as they may be separate positions, individuals, or roles depending on the country.
The authority of a head of government, such as a president, or prime minister and the relationship between that position and other state institutions, such as the relation between the head of state and of the
legislature, varies greatly among sovereign states, depending largely on the particular makeup of the government that has been chosen, won, or evolved over time.
parliamentary systems, including
constitutional monarchies, the head of government is the
de facto political leader of the government, and is answerable to
one chamber or the entire legislature. Although there is often a formal reporting relationship to a
head of state, the latter usually acts as a
figurehead who may take the role of chief executive on limited occasions, either when receiving
constitutional advice from the head of government or under specific provisions in a constitution. For example, in the United Kingdom, the prime minister "advises" the Queen on the appointment of the cabinet, advice she is required to accept. On the other hand, the Queen's long service as the head of state enables her to provide the prime minister with information and insight into many matters to better run the government. However, because the United Kingdom is a constitutional monarchy, the Prime Minister uses his or her own discretion regarding whether or not to follow the Queen's advice. The Queen also is entitled to appoint a new Prime Minister.
presidential republics or in
absolute monarchies, the head of state is also usually the head of government. The relationship between that leader and the government, however, can vary greatly, ranging from
separation of powers to
autocracy, according to the constitution (or other basic laws) of the particular state.
semi-presidential systems, the head of government may answer to both the head of state and the legislature, with the specifics provided by each country's constitution. A modern example is the present French government, which originated as the
French Fifth Republic in 1958. In France, the
president, the head of state, appoints the
prime minister, who is the head of government. However, the president must choose someone who can act effectively as an executive, but who also enjoys the support of the France's legislature, the
National Assembly, in order to be able to pass legislation. In some cases, the head of state may represent one political party but the majority in the National Assembly is of a different party. Given that the majority party has greater control over state funding and
primary legislation, the president is in effect forced to choose a prime minister from the opposition party in order to ensure an effective, functioning legislature. In this case, known as
cohabitation, the prime minister, along with the cabinet, controls domestic policy, with the president's influence largely restricted to foreign affairs.
directorial systems, the executive responsibilities of the head of government are spread among a group of people. A prominent example is the
Swiss Federal Council, where each member of the council heads a department and also votes on proposals relating to all departments.