This is a list of sovereign states by constitutionally-defined de jure system of government. This list does not measure the degree of democracy, political corruption, or state capacity of governments.

Parliamentary systems

Constitutional monarchies

These are systems in which the head of state is a constitutional monarch; the existence of their office and their ability to exercise their authority is established and restrained by constitutional law. Systems in which a prime minister is the active head of the executive branch of government. In some cases, the prime minister is also the leader of the legislature, while in other cases the executive branch is clearly separated from legislature (although the entire cabinet or individual ministers must step down in the case of a vote of no confidence). The head of state is a monarch who normally only exercises their powers with the consent of the government, the people and/or their representatives (except in emergencies, e.g. a constitutional crisis or a political deadlock).

Parliamentary republics

In a parliamentary republic, the head of government is selected or nominated by the legislature and is also accountable to it. The head of state is usually called a president and (in full parliamentary republics) is separate from the head of government, serving a largely apolitical, ceremonial role. In these systems, the head of government is usually called the prime minister, chancellor or premier. In mixed republican systems and directorial republican systems, the head of government also serves as head of state and is usually titled president. In some full parliamentary systems, the head of state is directly elected by voters. Under other classification systems, however, these systems may instead be classed as semi-presidential systems as presidents are always attached to a political party and may have broad powers (despite their weak presidency). Full parliamentary republican systems with presidents being purely ceremonial and neutral with no broad powers usually do not have a directly elected head of state and instead often use either an electoral college or a vote in the legislature to appoint the president.

Parliamentary republics with directly elected ceremonial heads of state

Parliamentary republics with indirectly elected ceremonial heads of state

Non-UN members or observers are in italics.

Parliamentary republics with an executive president

A combined head of state and head of government in the form of an executive president is either elected by the legislature or by the voters from among candidates nominated by the legislature (in the case of Kiribati), and they must maintain the confidence of the legislature to remain in office. In effect, "presidents" in this system function the same as prime ministers do in other parliamentary systems.

Presidential systems

In presidential systems a president is the head of government, and is elected and remains in office independently of the legislature. There is generally no prime minister, although if one exists, in most cases they serve purely at the discretion of the president.

Presidential republics without a prime minister

Non-UN members or observers are in italics.

Presidential republics with a prime minister

The following countries have presidential systems where the post of prime minister (official title may vary) exists alongside that of the president. The president is still both the head of state and government and the prime minister's role is mostly to assist the president. Non-UN members or observers are in italics.

Hybrid systems

Semi-presidential republics

In a semi-presidential republic a president exists alongside a prime minister and a cabinet, with the latter two being responsible to the legislature. It differs from a parliamentary system in that it has an executive president independent from the legislature; and from the presidential system in that the cabinet, although named by the president, is responsible to the legislature, which may force the cabinet to resign through a motion of no confidence.

Premier-presidential systems

In a premier-presidential system, the prime minister and cabinet are exclusively accountable to the legislature. Non-UN members or observers are in italics.

President-parliamentary systems

In a president-parliamentary system, the prime minister and cabinet are dually accountable to the president and the legislature. Non-UN members or observers are in italics.

Assembly-independent republics

A combined head of state and head of government (usually titled president) is elected by the legislature but is not held accountable to it (as is their cabinet), thus acting more independently from the legislature. They may or may not also hold a seat in the legislature.

Directorial republic

In a directorial republic, a council jointly exercises the powers and ceremonial roles of both the head of state and the head of government collectively. The council is elected by the parliament but is not subject to parliamentary confidence during its fixed term. The president is a member of the directorial council in a primus inter pares (first among equals) capacity and has no powers over other members of the directory.

Theocratic republic

Semi-constitutional monarchies

The prime minister is the nation's active executive, but the monarch still has considerable political powers that can be used at their own discretion.

Absolute monarchies

Specifically, monarchies in which the monarch's exercise of power is unconstrained by any substantive constitutional law. The monarch acts as both head of state and head of government. Non UN members or observers are in italics.

One-party states

States in which political power is by law concentrated within one political party whose operations are largely fused with the government hierarchy (in contrast to states where a multi-party system formally exists, but this fusion is achieved anyway through election fraud or underdeveloped multi-party traditions). Non-UN members or observers are in italics.

Military juntas

A committee of the nation's military leaders controls the government for the duration of a state of emergency. Constitutional provisions for government are suspended in these states; constitutional forms of government are stated in parentheses.

Provisional governments

States that have a system of government that is in transition or turmoil. These regimes lack a constitutional basis. Non-UN members or observers are in italics.

Systems of internal structure

Unitary states

A state governed as a single power in which the central government is ultimately supreme and any administrative divisions (sub-national units) exercise only the powers that the central government chooses to delegate. The majority of states in the world have a unitary system of government. Of the 193 UN member states, 126 are governed as centralized unitary states, and an additional 40 are regionalized unitary states.

Centralized unitary states

States in which most power is exercised by the central government. What local authorities do exist have few powers.

Regionalized unitary states

States in which the central government has delegated some of its powers to regional authorities, but where constitutional authority ultimately remains entirely at a national level.

Federation

States in which the national government shares power with regional governments with which it has legal or constitutional parity. The central government may or may not be (in theory) a creation of the regional governments.

European Union

The exact political character of the European Union is debated, some arguing that it is sui generis (unique), but others arguing that it has features of a federation or a confederation. It has elements of intergovernmentalism, with the European Council acting as its collective "president", and also elements of supranationalism, with the European Commission acting as its executive and bureaucracy.