The United Arab Republic (UAR; Arabic: الجمهورية العربية المتحدة, romanized: al-Jumhūriyya al-ʿArabiyya al-Muttaḥida) was a sovereign state in the Middle East from 1958 to 1971. It was initially a short-lived political union between Egypt (including Egyptian-governed Gaza) and Syria from 1958 until Syria seceded from the union following the 1961 Syrian coup d'état. Egypt continued to be known officially as the United Arab Republic until it was formally dissolved by Anwar Sadat in September 1971.

The republic was led by Gamal Abdel Nasser as the Egyptian president. The UAR was a member of the United Arab States, a loose confederation with the Mutawakkilite Kingdom of Yemen, which was dissolved in 1961. It was a brief pan-Arab union.

The United Arab Republic was established on 1 February 1958 as the first step towards a larger pan-Arab state, originally being proposed to Egyptian President Gamal Abdel Nasser by a group of political and military leaders in Syria.

Pan-Arab sentiment traditionally was very strong in Syria, and Nasser was a popular heroic figure throughout the Arab world following the 1956 Tripartite Aggression. There was thus considerable popular support in Syria for union with Nasser's Egypt. The Arab Socialist Ba'ath Party was the leading advocate of such a union.

In mid-1957, Western powers began to worry that Syria was close to a Communist takeover; it had a highly organized Communist Party and the newly appointed army's chief of staff, Afif al-Bizri, was a Communist sympathizer. This caused the Syrian Crisis of 1957 after which Syrians intensified their efforts to unite with Egypt. Nasser told a Syrian delegation, including President Shukri al-Quwatli and Prime Minister Khalid al-Azm, that they needed to rid their government of Communists, but the delegation countered and warned him that only total union with Egypt would end the "Communist threat". According to Abdel Latif Boghdadi, Nasser initially resisted a total union with Syria, favoring instead a federal union. However, Nasser was "more afraid of a Communist takeover" and agreed on a total merger. The increasing strength of the Syrian Communist Party, under the leadership of Khalid Bakdash, worried the Syrian Ba'ath Party, which was suffering from an internal crisis from which prominent members were anxious to find an escape. Syria had a democratic government since the overthrow of Adib Shishakli's military government in 1954, and popular pressure for Arab unity was reflected in the composition of parliament.

On 11 January 1958, the Syrian Chief of Staff Afif al-Bizri headed a Syrian delegation composed of military officers which came uninvited and unannounced to Cairo. The delegation was received by Egyptian Chief of Staff Abdel Hakim Amer and petitioned for a Syrian-Egyptian union. Only Syrian advocates of unity, including Salah al-Din al-Bitar and Akram al-Hourani had prior knowledge of this delegation; Quwatli and Azm were notified a day later and considered it tantamount to a "military coup".

Nasser's final terms for the union were decisive and non-negotiable: "a plebiscite, the dissolution of parties, and the withdrawal of the army from politics". While the plebiscite seemed reasonable to most Syrian elites, the latter two conditions were extremely worrisome. They believed it would destroy political life in Syria. Despite these concerns, the Syrian officials knew it was too late to turn back. Caught between Western and Soviet pressures, the members of the elite in Syria viewed the merger with Egypt as the least bad option to insulate from either side. They believed that Nasser's terms were unfair, but given the intense pressure that their government was undergoing, they believed that they had no other choice.

A plebiscite was held on 21 February 1958, with Egyptians and Syrians voting in favor of the merger. The result was announced on 22 February and Nasser was declared the new president of the United Arab Republic.