The Fundamental Law of Hungary (Hungarian: Magyarország alaptörvénye), the country's constitution, was adopted by parliament on 18 April 2011, promulgated by the president a week later and entered into force on 1 January 2012. It is Hungary's first constitution adopted within a democratic framework and following free elections.

The document succeeded the 1949 Constitution, originally adopted at the creation of the Hungarian People's Republic on 20 August 1949 and heavily amended on 23 October 1989. The 1949 Constitution was Hungary's first permanent written constitution and, until it was replaced, Hungary was the only former Eastern Bloc nation without an entirely new constitution after the end of communism.

Both domestically and abroad, the 2011 constitution has been the subject of controversy. Among the claims critics make are that it was adopted without sufficient input from the opposition and society at large, that it reflects the ideology of the ruling Fidesz party, and enshrines it in office, that it is rooted in a conservative Christian worldview despite Hungary not being a particularly devout country, and that it curtails and politicizes previously independent institutions. The government that enacted the charter has dismissed such assertions, saying it was enshrined lawfully and reflects the popular will.

The Fundamental Law is divided into sections and articles as outlined below.

Described as socially and fiscally conservative, the constitution initiates a number of changes. In an effort to push the public debt below 50% of gross domestic product (from above 80% at the time of adoption), the powers of the Constitutional Court on budget and tax matters are restricted until debt falls below 50%. The President is allowed to dissolve Parliament if a budget is not approved, and only companies with transparent activities and ownership structures are allowed to bid for government contracts. The powers of the head of the Hungarian National Bank are also limited, and the modification of tax and pension laws requires a two-thirds majority. The life of a fetus is protected from the moment of conception, and although the move is seen as opening the possibility for a future ban or restrictions on abortion, existing laws were unaffected. Same-sex couples may legally register their partnerships, but marriage is defined as being between one man and one woman. A ban on discrimination does not mention age or sexual orientation, and the constitution allows life imprisonment for violent crimes without the possibility of parole.

The constitution lowers judges' mandatory retirement age from 70 to the general retirement age, which was 62 at the time of adoption and is set to rise to 65 by 2022. The provision also covers prosecutors but exempts the Prosecutor General and the head of Hungary's highest court, the Curia. The country's name is changed from "Hungarian Republic" to "Hungary" but the country remains a republic. The preamble of the constitution contains references to the Holy Crown, God, Christianity, the fatherland and traditional family values. Laws affecting areas such as family policy, the pension system and taxation can be altered only through special legislation (cardinal acts) passed by a two-thirds majority of Parliament and are not subject to constitutional review.

For centuries, the Hungarian constitution was unwritten, based upon customary law. There was no civil code either; lawyers worked with the Corpus Iuris Hungarici. Among the laws that acquired constitutional force were a series of liberal statutes enacted during the 1848 Revolution; Statute XII of 1867 (enacting the Ausgleich); and further guarantees for constitutionalism, such as Statute IV of 1869, separating the executive and the judiciary; or the post-1870 statutes regulating local self-government and state administration.

Following the advent of the Hungarian Soviet Republic, the Revolutionary Governing Council adopted a Provisional Constitution on 2 April 1919, providing for a Soviet-style political system. On 23 June, the National Assembly of Allied Councils adopted Hungary's first charter-like constitution, the Constitution of the Socialist Allied Council Republic of Hungary. However, that regime was crushed two months later and Hungary returned to its historical, unwritten pre-1918 constitution.