The United Malays National Organisation (UMNO; Malay: Pertubuhan Kebangsaan Melayu Bersatu, PEKEMBAR) is a conservative and Malay nationalist political party in Malaysia. Founded in 1946 by Onn Jaafar, it is the oldest national political party in the country and has been described as Malaysia's "Grand Old Party". UMNO is a founding and principal member of the Barisan Nasional (BN) coalition, which, together with its predecessor the Alliance Party, governed Malaysia from the independence of Malaya in 1957 until its defeat in the 2018 general election. During this period, every Prime Minister of Malaysia was also the President of UMNO.

Following the 2018 election, UMNO retained considerable influence in Malaysian politics. It returned to power twice during the 2020–2022 Malaysian political crisis, first as part of a Perikatan Nasional–led government and later as the leading party in a BN–led administration. In the latter, UMNO Vice President Ismail Sabri Yaakob served as Prime Minister from 2021 to 2022. Since 2022, the party’s president, Ahmad Zahid Hamidi, has served as Deputy Prime Minister of Malaysia in a Pakatan Harapan–led government. Despite changes in coalition alignments, UMNO continues to play a significant role in shaping national policy and political discourse.

An ethnically based party advocating for Malay interests, UMNO's constitution states its objectives as the promotion of Malay nationalism, the concept of Ketuanan Melayu (lit. Malay Overlordship, or Malay Supremacy), the preservation of the "dignity" of the Malay people, the recognition of Islam as the religion of the federation and the protection of Malay culture as the core national culture of the country. The party also declares as a goal the defence and expansion of Islam within Malaysia. These aims are rooted in the party's longstanding position as the principal vehicle for Malay political representation at the national level.

In the 2018 leadership election, held after the party's general election defeat, former Deputy Prime Minister Ahmad Zahid Hamidi was elected UMNO president in a three-way contest. He defeated former UMNO Youth chief Khairy Jamaluddin and veteran leader Tengku Razaleigh Hamzah. The outcome was regarded by political observers as a defining moment in UMNO's post-defeat trajectory, setting the tone for its strategies in opposition and in subsequent coalition governments.

After the British returned to Malaya in the aftermath of World War II, the Malayan Union was formed. However, the Union was met with much opposition due to its constitutional framework, which allegedly threatened Malay sovereignty over Malaya.

The first phase of the journey of the UMNO party was the result of a combination of 41 Malay associations in the Malay Peninsula at that time led by Ahmad Boestamam who presented a memorandum to Sultan Ismail ibni Sultan Ibrahim who became the Sultan of Johor at that time to reject the Malayan Union proposal brought by the British.

In the second phase, a series of Malay congresses were held, culminating in the formation of the nationalist party, UMNO on 10 May 1946 at the Third Malay Congress in Johor Bahru, with Onn Jaafar as its leader. UMNO strongly opposed the Malayan Union, but originally did not seek political power. UMNO had no choice but continue playing a supporting role to the British colonial administration. The British cooperated with UMNO leaders and helped to defeat the communist insurgency.

In 1949, after the Malayan Union had been replaced by the semi-autonomous Federation of Malaya, UMNO shifted its focus to politics and governance. According to at least one official school textbook published during UMNO's time in government, the party fought for other races once they were at the helm of the country.