An uncodified constitution is a type of constitution where the fundamental rules often take the form of customs, usage, precedent and a variety of statutes and legal instruments. An understanding of the constitution is obtained through reading commentary by the judiciary, government committees or legal experts. In such a constitutional system, all these elements may be (or may not be) recognized by courts, legislators and the bureaucracy as binding upon government and limiting its powers. Such a framework is sometimes imprecisely called an "unwritten constitution"; however, all the elements of an uncodified constitution are typically written down in a variety of official documents, though not codified in a single document.
An uncodified constitution has the advantages of elasticity, adaptability and resilience, A. V. Dicey described the uncodified constitution as "the most flexible polity in existence." A significant disadvantage, however, is that controversies may arise due to different understandings of the usages and customs that form the fundamental provisions of the constitution.
A new condition or situation of government may be resolved by precedent or passing legislation. Unlike a codified constitution, there are no special procedures for making a constitutional law and it will not be inherently superior to other legislation. A country with an uncodified constitution lacks a specific moment where the principles of its government were deliberately decided. Instead, these are allowed to evolve according to the political and social forces arising throughout its history.
When viewed as a whole system, the difference between a codified and uncodified constitution is one of degree. Any codified constitution will be overlaid with supplementary legislation and customary practice after a period of time. Conversely, customs and practices that have been observed for long periods in an uncodified manner may be added to the written constitution at various junctures, such as in the case of the 2-term limit for Presidents of the United States. This custom was observed for nearly a century and a half, unbroken, without any enforcement mechanism until it was ignored by Franklin Roosevelt, after which it was added to the written Constitution as mandatory de jurecode: lat promoted to code: la .
The following states can be considered to have an uncodified constitution:
- Canada: Although there are Constitution Acts, important aspects of the constitutional system are uncodified. The preamble to the Constitution of Canada declares it to be "similar in principle to that of the United Kingdom" (which is uncodified). This applies at the federal level and to the provinces, although each does have the power to modify or enact their own within their exclusive areas of responsibility. To date only British Columbia has enacted a codified provincial constitution (see Constitution of British Columbia), though the other provinces' roles and powers are spelled out in section 93 of the Constitution Act, 1867, and through amendments to it dealing with particular provinces such as the Manitoba Act and the Newfoundland Act. See Constitution of Canada.
- China: Some Chinese academics including legal theorist Jiang Shigong have argued that China has both a written constitution and an unwritten constitution based on the comprehensive leadership of the Communist Party.
- Israel: the declaration of independence promised a constitution by 2 October 1948, but due to irreconcilable differences in the Knesset, no complete codified constitution has been written yet. There are several Basic Laws, however. See Constitution of Israel.
- New Zealand: New Zealand has no single constitutional document. It is an uncodified constitution, sometimes referred to as an "unwritten constitution", although the New Zealand constitution is in fact an amalgamation of written and unwritten sources. The Constitution Act 1986 has a central role, alongside a collection of other statutes, orders in Council, letters patent, decisions of the courts, principles of the Treaty of Waitangi, and unwritten traditions and conventions. See Constitution of New Zealand.
- San Marino: San Marino has several documents that make up its constitution, including some lasting centuries. See Constitution of San Marino.
- Saudi Arabia: Saudi Arabia has no legally binding written constitution. In 1960, King Faisal declared the Quran, the religious text of Islam, to be the constitution. See Constitution of Saudi Arabia. However, in 1992, the Basic Law of Saudi Arabia was adopted by royal decree.
- United Kingdom: there is no defining document that can be termed "the constitution". Because the political system evolved over time, rather than being changed suddenly in an event such as a revolution, collapse of government or overthrow of monarchy, it is continuously being defined by acts of Parliament and decisions of the Law Courts (see Constitution of the United Kingdom). The closest the UK has come to a constitutional code has been the Treaty of Union 1707. Due to the United Kingdom having an uncodified constitution, many acts have been added to the collection of constitutional statutes,[clarification needed] e.g. The Freedom of Information Act 2000, the Human Rights Act 1998 and the Fixed-term Parliaments Act 2011. This means the United Kingdom's constitutional rules are not written in a single document, but not that it has an "unwritten" constitution.
- The Constitution of the Roman Republic, made up of the Twelve Tables and other statutes.
- Hungary had an uncodified constitution prior to 1949.
- Sweden: What written and unwritten elements made up the Swedish constitution was the subject of much uncertainty and debate, until the Instrument of Government 1809 (1809 års regeringsform) made a point of expressly superseding “all more or less valid constitutions ... as well as ... any other such laws, acts, ordnances, statutes or decisions, however ancient or new, as have previously been included under the name of constitution”. As of 2021, the Instrument of Government specifies at paragraph 3 that the constitution of Sweden (rikets grundlagar) consists of the Instrument of Government, the Freedom of the Press Act, the Fundamental Law on Freedom of Expression and the Act of Succession.
- The Constitution of the Grand Principality of Finland was never codified. The Emperor of Russia, who also served from 1809 to 1917 as Grand Prince of Finland, never specifically recognized the Constitution as that of a separate and autonomous Finland, in spite of the fact that that Constitution largely dictated the relationship between Finland and the Russian Empire throughout the Russian era in Finland. By the late 19th century leading Finnish intellectuals—liberals and nationalists, and later, socialists as well—had come to consider Finland as a constitutional state in its own right in a mere real union with Russia. This notion clashed with emerging Russian nationalism and with Russian calls for a unitary state for Slavs only, which eventually came into conflict with Finnish separatism and constitutionalism in the form of "russification policies", which restricted Finland's extensive autonomy from 1899 onwards, excluding a brief interruption between 1905 and 1908, all the way to the February Revolution in 1917. The Russian Provisional Government of 1917 eventually recognized the Finnish constitution, and after the October Revolution the Bolshevik government of the RSFSR recognized Finland's declaration of independence on New Year's Eve 1917.
- The French Third Republic had an uncodified constitution. Several constitutional texts were adopted in the few years after the proclamation of the Republic in 1870 but in practice the institutions did not follow them, and the true organization of powers was made through custom. It remains as of 2020 the longest lasting French constitution since the Revolution of 1789.
- The Constitution of Queensland before 2001
- Oman prior to 1996
- Libya between 1969 and 1975
- Thailand prior to 1932 had Dharmaśāstra of Manu as an uncodified constitution.
- Johari, J. C. (2006) New Comparative Government, Lotus Press, New Delhi, p. 167–169
- A. V. Dicey, An Introduction to the Study of the Law of the Constitution (page 39)
- Prabir Kumar De (2011) Comparative Politics, Dorling Kindersley, p. 59
- Constitution Acts, 1867 to 1982, being The Constitution Act, 1867 (UK), 30 & 31 Vict., c. 3, and The Constitution Act, 1982, Schedule B to the Canada Act 1982 (UK), 1982, c. 11.
- Ontario (Attorney General) v. OPSEU,  2 S.C.R. 2, 1987 CanLII 71 (SCC), Retrieved 2019-11-07.
- Zhai, Han (2018). "The 'Invisible Constitution' seen Realistically: Visualising China's Unitary System". In Dixon, Rosalind; Stone, Adrienne (eds.). The Invisible Constitution in Comparative Perspective. p. 406. ISBN 9781108417570.
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- Joseph, Philip (1989). "Foundations of the Constitution" (PDF). Canterbury Law Review. p. 72.
- Eichbaum, Chris; Shaw, Richard (2005). Public Policy in New Zealand - Institutions, processes and outcomes. Pearson Education New Zealand. pp. 32–33. ISBN 1877258938.
- Palmer, Matthew (20 June 2012). "Constitution - What is a constitution?". Te Ara: The Encyclopedia of New Zealand. Retrieved 16 August 2019.
- Palmer, Matthew (2008). The Treaty of Waitangi in New Zealand's Law and Constitution. Victoria University of Wellington Press. p. 17. ISBN 978-0-86473-579-9.
- Champion, Daryl (2003). The paradoxical kingdom: Saudi Arabia and the momentum of reform. p. 60. ISBN 978-1-85065-668-5.
- Robbers, Gerhard (2007). Encyclopedia of world constitutions. 2. p. 791. ISBN 978-0-8160-6078-8.
- King, A (2007). The British Constitution. Oxford: Oxford University Press. p. 6.
- Bull, Thomas; Sterzel, Fredrik (2020). Regeringsformen: en kommentar (4th ed.). Lund: Studentlitteratur. p. 52.