The separation of powers is a model for the governance of a state. Under this model, a state's government is divided into branches, each with separate and independent powers and areas of responsibility so that the powers of one branch are not in conflict with the powers associated with the other branches. The typical division is into three branches: a legislature, an executive, and a judiciary, which is the trias politica model. It can be contrasted with the fusion of powers in parliamentary systems and semi-presidential systems where the executive and legislative branches overlap.

Separation of powers, therefore, refers to the division of responsibilities into distinct branches to limit any one branch from exercising the core functions of another. The intent of separation of powers is to prevent the concentration of unchecked power by providing for "checks" and "balances" to avoid autocracy, over-reaching by one branch over another, and the attending efficiency of governing by one actor without need for negotiation and compromise with any other.

The separation of powers model is often imprecisely and metonymically used interchangeably with the trias politica principle. While the trias politica is a common type of model, there are governments which utilize bipartite, rather than tripartite, systems as mentioned later in the article.

Aristotle first mentioned the idea of a "mixed government" or hybrid government in his work Politics where he drew upon many of the constitutional forms in the city-states of Ancient Greece. In the Roman Republic, the Roman Senate, Consuls and the Assemblies showed an example of a mixed government according to Polybius (Histories, Book 6, 11–13).

John Calvin (1509–1564) favoured a system of government that divided political power between democracy and aristocracy (mixed government). Calvin appreciated the advantages of democracy, stating: "It is an invaluable gift if God allows a people to elect its own government and magistrates."^[1] In order to reduce the danger of misuse of political power, Calvin suggested setting up several political institutions which should complement and control each other in a system of checks and balances.^[2]

In this way, Calvin and his followers resisted political absolutism and furthered the growth of democracy. Calvin aimed to protect the rights and the well-being of ordinary people.^[3] In 1620, a group of English separatist Congregationalists and Anglicans (later known as the Pilgrim Fathers) founded Plymouth Colony in North America. Enjoying self-rule, they established a bipartite democratic system of government. The "freemen" elected the General Court, which functioned as legislature and judiciary and which in turn elected a governor, who together with his seven "assistants" served in the functional role of providing executive power.^[4] Massachusetts Bay Colony (founded 1628), Rhode Island (1636), Connecticut (1636), New Jersey, and Pennsylvania had similar constitutions – they all separated political powers. (Except for Plymouth Colony and Massachusetts Bay Colony, these English outposts added religious freedom to their democratic systems, an important step towards the development of human rights.^[5][6]) Books like William Bradford's History of Plymoth Plantation (written between 1630 and 1651) were widely read in England. So the form of government in the colonies was well known in the mother country, including to the philosopher John Locke (1632–1704). He deduced from a study of the English constitutional system the advantages of dividing political power into the legislative (which should be distributed among several bodies, for example, the House of Lords and the House of Commons), on the one hand, and the executive and federative power, responsible for the protection of the country and prerogative of the monarch, on the other hand. (The Kingdom of England had no written constitution.)^[7]

The term "tripartite system" is commonly ascribed to French Enlightenment political philosopher Baron de Montesquieu, although he did not use such a term. In reality he referred to "distribution" of powers. In The Spirit of the Laws (1748), Montesquieu described the various forms of distribution of political power among a legislature, an executive, and a judiciary. Montesquieu's approach was to present and defend a form of government which was not excessively centralized in all its powers to a single monarch or similar ruler, form of government known then as "aristocracy". He based this model on the Constitution of the Roman Republic and the British constitutional system. Montesquieu took the view that the Roman Republic had powers separated so that no one could usurp complete power.^[8][9][10] In the British constitutional system, Montesquieu discerned a separation of powers among the monarch, Parliament, and the courts of law.

Montesquieu argues that each Power should only exercise its own functions, it was quite explicit here:

Separation of powers requires a different source of legitimization, or a different act of legitimization from the same source, for each of the separate powers. If the legislative branch appoints the executive and judicial powers, as Montesquieu indicated, there will be no separation or division of its powers, since the power to appoint carries with it the power to revoke.

Montesquieu did actually specify that the independence of the judiciary has to be real, and not merely apparent.^[13] The judiciary was generally seen as the most important of the three powers, independent and unchecked,^[14] while also likely to claim to be the least dangerous one.^[13]

Checks and balances is the principle that each of the Branches has the power to limit or check the other two and this creates a balance between the three separate powers of the state, this principle induces that the ambitions of one branch prevent that one of the other branches becomes supreme, and thus be eternally confronting each other and in that process leaving the people free from government abuses.

Immanuel Kant was an advocate of this, noting that "the problem of setting up a state can be solved even by a nation of devils" so long as they possess an appropriate constitution to pit opposing factions against each other.^[15]

Checks and Balances are designed to maintain the system of separation of powers keeping each branch in its place. This is based on the idea that it is not enough to separate the powers and guarantee their independence but to give the various branches the constitutional means to defend their own legitimate powers from the encroachments of the other branches.^[16] They guarantee that the powers of the state have the same weight (co-equal), that is, to be balanced, so that they can limit each other, avoiding the abuse of state power. The origin of checks and balances, like separation of powers itself, is specifically credited to Montesquieu in the Enlightenment (in The Spirit of the Laws, 1748), under this influence was implemented in 1787 in the Constitution of the United States.

The following example of the separation of powers and their mutual checks and balances for the experience of the United States Constitution is presented as illustrative of the general principles applied in similar forms of government as well.

Constitutions with a high degree of separation of powers are found worldwide. The UK system is distinguished by a particular entwining of powers.^[19] A number of Latin American countries have electoral branches of government.

Countries with little separation of power include New Zealand and Canada. Canada makes limited use of separation of powers in practice, although in theory it distinguishes between branches of government.

New Zealand's constitution is based on the principle of separation of powers through a series of constitutional safeguards, many of which are tacit. The Executive's ability to carry out decisions often depends on the Legislature, which is elected under the mixed member proportional system. This means the government is rarely a single party but a coalition of parties. The Judiciary is also free of government interference. If a series of judicial decisions result in an interpretation of the law which the Executive considers does not reflect the intention of the policy, the Executive can initiate changes to the legislation in question through the Legislature. The Executive cannot direct or request a judicial officer to revise or reconsider a decision; decisions are final. Should there be a dispute between the Executive and Judiciary, the Executive has no authority to direct the Judiciary, or its individual members and vice versa.

Complete separation of powers systems are almost always presidential, although theoretically this need not be the case. There are a few historical exceptions, such as the Directoire system of revolutionary France. Switzerland offers an example of non-Presidential separation of powers today: It is run by a seven-member executive branch, the Federal Council. However, some might argue that Switzerland does not have a strong separation of powers system, as the Federal Council is appointed by parliament (but not dependent on parliament) and although the judiciary has no power of review, the judiciary is still separate from the other branches.

Australia does not maintain a strict separation between the legislative and executive branches of government—indeed, government ministers are required to be members of parliament—but the federal judiciary strictly guards its independence from the other two branches. However, under influence from the US constitution, the Australian constitution does define the three branches of government separately, and this has been interpreted by the judiciary to induce an implicit separation of powers.^[20] State governments have a similar level of separation of power, but this is generally on the basis of convention, rather than constitution.

The Constitution of Austria was originally written by Hans Kelsen, the prominent constitutional scholar in Europe at that time. Kelsen was to serve as a part of the judicial court of review for Austria as part of its tripartite government.

The Constitution of the Czech Republic, adopted in 1992 immediately before the dissolution of Czechoslovakia, establishes the traditional tripartite division of powers^[21] and continues the tradition of its predecessor constitutions. The Czechoslovak Constitution of 1920, which replaced the provisional constitution adopted by the newly independent state in 1918, was modeled after the constitutions of established democracies such as those of the United Kingdom, United States and France, and maintained this division,^[22] as have subsequent changes to the constitution that followed in 1948 with the Ninth-of-May Constitution, the 1960 Constitution of Czechoslovakia as well as the Constitutional Act on the Czechoslovak Federation of 1968.

According to the Constitution of the Fifth Republic, the government of France^[23] is divided into three branches:

Hong Kong is a Special Administrative Region established in 1997 pursuant to the Sino-British Joint Declaration, an international treaty made between Britain and China in 1984, registered with the United Nations. Currently, Hong Kong has three branches of government as codified in the Basic Law, its constitution, which largely preserved political structures of the British colonial era, under the doctrine of one country, two systems:

The Chief Executive, elected by a 1200-member Election Committee which historically was dominated by pro-Beijing establishment members, is both head of the region and head of government, and chairs the Executive Council which is composed of "unofficial" members and government secretaries.

The legislature consists of 70 members, 35 of whom are elected by "functional" constituencies represented by members within various industries rather than the public at large.^[25] Separation of power between executive and legislature is, therefore, questionable.^[26]

The courts frequently exercise a power of judicial review of administrative actions and also decide matters of constitutionality of legislation, though this power is circumscribed under the power of the People's Republic of China's National People's Congress to make final determinations as to interpretation.^[27] Hence, the separation of powers is again structurally weak.

It is worth noting that the branches' separation of power may not be intended within the Hong Kong Basic Law as leaders of the PRC have publicly called for the three branches to cooperate and be led by the Chief Executive.^[28]

Further, Deng Xiaoping was quoted to have categorically dismissed Hong Kong having a "Trias Politica" system.^[29]

India follows constitutional democracy which offers a clear separation of powers. The judiciary branch is fairly independent of the other two branches with the power to interpret the constitution. Parliament has the legislative powers. Executive powers are vested with the President who is advised by the Union Council of Ministers headed by the Prime Minister. The constitution of India vested the duty of protecting, preserving and defending the constitution with the President as common head of the executive, parliament, armed forces, etc. not only for the union government but also the various state governments in a federal structure. All three branches have "checks and balances" over each other to maintain the balance of power and not to exceed the constitutional limits.^[30]

In Italy the powers are separated, even though the Council of Ministers needs a vote of confidence from both chambers of Parliament, that represents a large number of members (almost 1,000).^[31]

Like every parliamentary form of government, there is no real separation between Legislature and Executive, rather a continuum between them due to the confidence link. By the way, the balance is protected by Constitution also between these two branches.^[32] and, obviously, between them and the judiciary branch, which is really independent.

A note on the status of separation of power, checks and balances, and balance of power in Norway today.^[33]

In the original constitution of 1814 the Montesquieu concept was enshrined, and the people at the time had the same skepticism about political parties as the American founding fathers and the revolutionaries in France. Nor did people really want to get rid of the king and the Council of State (privy council). King and council was a known concept that people had lived with for a long time and was for the most part comfortable with. The 1814 constitution came about as a reaction to external events, most notable the Treaty of Kiel see 1814 in Norway. There was no revolution against the current powers that had been the case in the US and France.

As there was no election of the executive, the king reigned supremely independent in selecting the members of the Council of State, no formal political parties formed until the 1880s. A conflict between the executive and legislature started developing in the 1870s and climaxed with the legislature impeaching the entire Council of State in 1884. (See Statsrådssaken (Norwegian Wikipedia page))

With this came a switch to a parliamentary system of government and while the full process takes decades, it has led to a system of parliamentary sovereignty where the Montesquieu idea of separation of powers is technically dead even though the three branches remain important institutions.

This does not mean that there are no checks and balances. With the introduction of a parliamentary system, political parties started to form quickly and this led to a call for electoral reform that saw the introduction of a Party-list proportional representation in 1918. The peculiarities of the Norwegian election system generate 6–8 parties and make it extremely difficult for a single party to gain an absolute majority. It has only occurred for a brief period in the aftermath of World War II where the Labour Party had an absolute majority.

A multi-party system parliament that must either form a minority executive or a coalition executive function as a perfectly good system of checks and balances even if it was never a stated goal for the introduction of multiparty system. The multiparty system came about in response to a public outcry of having too few parties and a general feeling of a lack of representation. For this reason you'll find very little on the topic of separation of powers or checks and balances in the works of Norwegian political sciences today.

The development of the British constitution, which is not a codified document, is based on this fusion in the person of the Monarch, who has a formal role to play in the legislature (Parliament, which is where legal and political sovereignty lies, is the Crown-in-Parliament, and is summoned and dissolved by the Sovereign who must give his or her Royal Assent to all Bills so that they become Acts), the executive (the Sovereign appoints all ministers of His/Her Majesty's Government, who govern in the name of the Crown) and the judiciary (the Sovereign, as the fount of justice, appoints all senior judges, and all public prosecutions are brought in his or her name).

Although the doctrine of separation of power plays a role in the United Kingdom's constitutional doctrine, the UK constitution is often described as having "a weak separation of powers" A. V. Dicey, despite its constitution being the one to which Montesquieu originally referred. For example, in the United Kingdom, the executive forms a subset of the legislature, as did—to a lesser extent—the judiciary until the establishment of the Supreme Court of the United Kingdom. The Prime Minister, the Chief Executive, sits as a member of the Parliament of the United Kingdom, either as a peer in the House of Lords or as an elected member of the House of Commons (by convention, and as a result of the supremacy of the Lower House, the Prime Minister now sits in the House of Commons) and can effectively be removed from office by a simple majority vote. Furthermore, while the courts in the United Kingdom are amongst the most independent in the world, the Law Lords, who were the final arbiters of judicial disputes in the UK sat simultaneously in the House of Lords, the upper house of the legislature, although this arrangement ceased in 2009 when the Supreme Court of the United Kingdom came into existence. Furthermore, because of the existence of Parliamentary sovereignty, while the theory of separation of powers may be studied there, a system such as that of the UK is more accurately described as a "fusion of powers".

Until 2005, the Lord Chancellor fused the Legislature, Executive and Judiciary, as he was the ex officio Speaker of the House of Lords, a Government Minister who sat in Cabinet and was head of the Lord Chancellor's Department which administered the courts, the justice system and appointed judges, and was the head of the Judiciary in England and Wales and sat as a judge on the Judicial Committee of the House of Lords, the highest domestic court in the entire United Kingdom, and the Judicial Committee of the Privy Council, the senior tribunal court for parts of the Commonwealth. The Lord Chancellor also had certain other judicial positions, including being a judge in the Court of Appeal and President of the Chancery Division. The Lord Chancellor combines other aspects of the constitution, including having certain ecclesiastical functions of the established state church, making certain church appointments, nominations and sitting as one of the thirty-three Church Commissioners. These functions remain intact and unaffected by the Constitutional Reform Act. In 2005, the Constitutional Reform Act separated the powers with Legislative functions going to an elected Lord Speaker and the Judicial functions going to the Lord Chief Justice. The Lord Chancellor's Department was replaced with a Ministry of Justice and the Lord Chancellor currently serves in the position of Secretary of State for Justice.

The judiciary has no power to strike down primary legislation, and can only rule on secondary legislation that it is invalid with regard to the primary legislation if necessary.

Under the concept of parliamentary sovereignty, Parliament can enact any primary legislation it chooses. However, the concept immediately becomes problematic when the question is asked; "If parliament can do anything, can it bind its successors?". It is generally held that parliament can do no such thing.

Equally, while statute takes precedence over precedent-derived common law and the judiciary has no power to strike down primary legislation, there are certain cases where the supreme judicature has effected an injunction against the application of an act or reliance on its authority by the civil service. The seminal example of this is the Factortame case, where the House of Lords granted such an injunction preventing the operation of the Merchant Shipping Act 1988 until litigation in the European Court of Justice had been resolved.

The House of Lords ruling in Factortame (No. 1), approving the European Court of Justice formulation that "a national court which, in a case before it concerning Community law, considers that the sole obstacle which precludes it from granting interim relief is a rule of national law, must disapply that rule", has created an implicit tiering of legislative reviewability; the only way for parliament to prevent the supreme judicature from injunctively striking out a law on the basis of incompatibility with Community law is to pass an act specifically removing that power from the court, or by repealing the European Communities Act 1972.

The British legal systems are based on common law traditions, which require:

Separation of powers was first established in the United States Constitution, wherein the founding fathers included features of many new concepts, including hard-learned historical lessons about the checks and balances of power. Similar concepts were also prominent in the state governments of the United States. As colonies of Great Britain, the founding fathers considered that the American states had suffered an abuse of the broad power of parliamentarism and monarchy. As a remedy, the United States Constitution limits the powers of the federal government through various means—in particular, the three branches of the federal government are divided by exercising different functions. The executive and legislative powers are separated in origin by separate elections, and the judiciary is kept independent. Each branch controls the actions of others and balances its powers in some way.

In the Constitution, Article 1 Section I grants Congress only those "legislative powers herein granted" and proceeds to list those permissible actions in Article I Section 8, while Section 9 lists actions that are prohibited for Congress. The vesting clause in Article II places no limits on the Executive branch, simply stating that "The Executive Power shall be vested in a President of the United States of America."^[34] The Supreme Court holds "The judicial Power" according to Article III, and judicial review was established in Marbury v. Madison under the Marshall court.^[35]

The presidential system adopted by the Constitution of the United States obeys the balance of powers sought, and not found, by the constitutional monarchy. The people appoint their representatives to meet periodically in a legislative body, and, since they do not have a king, the people themselves elect a preeminent citizen to perform, also periodically, the executive functions of the State. The direct election of the head of state or of the executive power is an inevitable consequence of the political freedom of the people, understood as the capacity to appoint and depose their leaders. Only this separate election of the person who has to fulfill the functions that the Constitution attributes to the president of the government, so different by its nature, and by its function, from the election of representatives of the electors, allows the executive power to be controlled by the legislative and submitted to the demands of political responsibility.^[36]

Judicial independence is maintained by appointments for life which remove any dependence on the Executive, with voluntary retirement and a high threshold for dismissal by the Legislature, in addition to a salary that cannot be diminished during their service.

The federal government refers to the branches as "branches of government", while some systems use "government" exclusively to describe the executive. The Executive branch has attempted^[37] to claim power arguing for separation of powers to include being the Commander-in-Chief of a standing army since the American Civil War, executive orders, emergency powers, and security classifications since World War II, national security, signing statements, and the scope of the unitary executive.

According to Sun Yat-sen's idea of "separation of the five powers", the government of the Republic of China has five branches:

The president and vice president as well as the defunct National Assembly are constitutionally not part of the above five branches. Before being abolished in 2005, the National Assembly was a standing constituent assembly and electoral college for the president and vice president. Its constitutional amending powers were passed to the legislative yuan and its electoral powers were passed to the electorate.

The relationship between the executive and legislative branches are poorly defined. An example of the problems this causes is the near complete political paralysis that results when the president, who has neither the power to veto nor the ability to dissolve the legislature and call new elections, cannot negotiate with the legislature when his party is in the minority.^[38] The examination and control yuans are marginal branches; their leaders as well as the leaders of the executive and judicial yuans are appointed by the president and confirmed by the legislative yuan. The legislature is the only branch that chooses its own leadership. The vice president has practically no responsibilities.

Belgium is currently a federated state that has imposed the trias politica on different governmental levels. The constitution of 1831, considered one of the most liberal of its time for limiting the powers of its monarch and imposing a rigorous system of separation of powers, is based on three principles (represented in the Schematic overview of Belgian institutions):

Trias Politica (horizontal separation of powers):

Subsidiarity (vertical separation of powers):

Secularism (separation of state and religion):

In the aftermath of the 43-day civil war in 1948 (after former President and incumbent candidate Rafael Ángel Calderón Guardia tried to take power through fraud, by not recognising the results of the presidential election that he had lost), the question of which transformational model the Costa Rican State would follow was the main issue that confronted the victors. A Constituent Assembly was elected by popular vote to draw up a new constitution, enacted in 1949, and remains in force. This document was an edit of the constitution of 1871, as the constituent assembly rejected more radical corporatist ideas proposed by the ruling Junta Fundadora de la Segunda República (which, although having come to power by military force, abolished the armed forces). Nonetheless, the new constitution increased centralization of power at the expense of municipalities and eliminated provincial government altogether, at the time it increased the powers of congress and the judiciary.

It established the three supreme powers as the legislature, executive, and judicial branches, but also created two other autonomous state organs that have equivalent power, but not equivalent rank. The first is the Tribunal Supremo de Elecciones de Costa Rica (electoral branch) which controls elections and makes unique, unappealable decisions on their outcomes.

The second is the office of the Comptroller General (audit branch), an autonomous and independent organ nominally subordinate to the unicameral legislative assembly. All budgets of ministries and municipalities must pass through this agency, including the execution of budget items such as contracting for routine operations. The Comptroller also provides financial vigilance over government offices and office holders, and routinely brings actions to remove mayors for malfeasance, firmly establishing this organization as the fifth branch of the Republic.

The European Union is a supranational polity, and is neither a country nor a federation; but as the EU wields political power it complies with the principle of separation of powers. There are seven institutions of the European Union. In intergovernmental matters, most power is concentrated in the Council of the European Union—giving it the characteristics of a normal international organization. Here, all power at the EU level is in one branch. In the latter there are four main actors. The European Commission acts as an independent executive which is appointed by the Council in conjunction with the European Parliament; but the Commission also has a legislative role as the sole initiator of EU legislation.^{[39][40] [41]} An early maxim was: "The Commission proposes and the Council disposes"; and although the EU's lawmaking procedure is now much more complicated, this simple maxim still holds some truth. As well as both executive and legislative functions, the Commission arguably exercises a third, quasi-judicial, function under Articles 101 & 102 TFEU (competition law ); although the ECJ remains the final arbiter. The European Parliament is one half of the legislative branch and is directly elected. The Council itself acts both as the second half of the legislative branch and also holds some executive functions (some of which are exercised by the related European Council in practice). The European Court of Justice acts as the independent judicial branch, interpreting EU law and treaties. The remaining institution, the European Court of Auditors, is an independent audit authority (due to the sensitive nature of fraud in the EU).

The three branches in German government are further divided into six main bodies enshrined in the Basic Law for the Federal Republic of Germany:

Besides the constitutional court the judicial branch at the federal level is made up of five supreme courts—one for civil and criminal cases (Bundesgerichtshof), and one each for administrative, tax, labour, and social security issues. There are also state (Länder / Bundesländer) based courts beneath them, and a rarely used senate of the supreme courts.

The four independent branches of power in Hungary (the parliament, the government, the court system, and the office of the public accuser) are divided into six bodies:

The independent pillar status of the Hungarian public accuser's office is a unique construction, loosely modeled on the system Portugal introduced after the 1974 victory of the Carnation Revolution. The public accuser (attorney general) body has become the fourth column of Hungarian democracy only in recent times: after communism fell in 1989, the office was made independent by a new clausule XI. of the Constitution. The change was meant to prevent abuse of state power, especially with regards to the use of false accusations against opposition politicians, who may be excluded from elections if locked in protracted or excessively severe court cases.

To prevent the Hungarian accuser's office from neglecting its duties, natural human private persons can submit investigation requests, called "pótmagánvád" directly to the courts, if the accusers' office refuses to do its job. Courts will decide if the allegations have merit and order police to act in lieu of the accuser's office if warranted. In its decision No. 42/2005 the Hungarian constitutional court declared that the government does not enjoy such privilege and the state is powerless to further pursue cases if the public accuser refuses to do so.

Notable examples of states after Montesquieu that had more than three powers include: