Nakba Day (Arabic: ذكرى النكبة, romanized: Dhikra an-Nakba, lit. 'Memory of the Catastrophe') is the day of commemoration for the Nakba, also known as the Palestinian Catastrophe, which comprised the destruction of Palestinian society and homeland in 1948, and the permanent displacement of a majority of the Palestinian people. It is generally commemorated on 15 May, the Gregorian calendar date of the Israeli Declaration of Independence in 1948. For Palestinians, it is an annual day of commemoration of the displacement that preceded and followed Israel's establishment.

The day was officially inaugurated by Yasser Arafat in 1998, though the date had been unofficially used for protests since as early as 1949.

Nakba Day is generally commemorated on 15 May, the day after the Gregorian calendar date for Israel's Independence. In Israel, Nakba Day events have been held by some Arab citizens on Yom Ha'atzmaut (Israel's Independence Day), which is celebrated in Israel on the Hebrew calendar date (5 Iyar or shortly before or after). Because of the differences between the Hebrew and the Gregorian calendars, Independence Day and the official 15 May date for Nakba Day usually only coincide every 19 years.

As early as 1949, one year after the establishment of the State of Israel, 15 May was marked in several West Bank cities (under Jordanian rule) by demonstrations, strikes, the raising of black flags, and visits to the graves of people killed during the 1948 war. These events were organized by worker and student associations, cultural and sports clubs, scouts clubs, committees of refugees, and the Muslim Brotherhood. The speakers in these gatherings blamed the Arab governments and the Arab League for failing to "save Palestine", according to author Tamir Sorek. By the late 1950s, 15 May would be known in the Arab world as Palestine Day, mentioned by the media in Arab and Muslim countries as a day of international solidarity with Palestine.

Commemoration of the Nakba by Arab citizens of Israel who are internally displaced persons as a result of the 1948 war has been practiced for decades, but until the early 1990s was relatively weak. Initially, the memory of the catastrophe of 1948 was personal and communal in character and families or members of a given village would use the day to gather at the site of their former villages. Small scale commemorations of the tenth anniversary in the form of silent vigils were held by Arab students at a few schools in Israel in 1958, despite attempts by the Israeli authorities to thwart them. Visits to the sites of former villages became increasingly visible after the events of Land Day in 1976. In the wake of the failure of the 1991 Madrid Conference to broach the subject of refugees, the Association for the Defense of the Rights of the Internally Displaced in Israel was founded to organize a March of Return to the site of a different village every year on 15 May so as to place the issue on the Israeli public agenda.

By the early 1990s, annual commemorations of the day by Palestinian Arab citizens of Israel held a prominent place in the community's public discourse.

Meron Benvenisti writes that it was "…Israeli Arabs who taught the residents of the territories to commemorate Nakba Day." Palestinians in the occupied territories were called upon to commemorate 15 May as a day of national mourning by the Palestine Liberation Organization's United National Command of the Uprising during the First Intifada in 1988. The day was inaugurated by Yasser Arafat in 1998.

The event is often marked by speeches and rallies by Palestinians in Israel, the West Bank and Gaza, in Palestinian refugee camps in Arab states, and in other places around the world. Protests at times develop into clashes between Palestinians and the Israel Defense Forces in the West Bank and Gaza Strip. In 2003 and 2004, there were demonstrations in London and New York City. In 2002, Zochrot was established to organize events raising the awareness of the Nakba in Hebrew so as to bring Palestinians and Israelis closer to a true reconciliation. The name is the Hebrew feminine plural form of "remember".

On Nakba Day 2011, Palestinians and other Arabs from the West Bank, Gaza Strip, Lebanon and Syria marched towards their respective borders, or ceasefire lines and checkpoints in Israeli-occupied territories, to mark the event. At least twelve Palestinians and supporters were killed and hundreds wounded as a result of shootings by the Israeli Army. The Israeli army opened fire after thousands of Syrian protesters tried to forcibly enter the Israeli-occupied Golan Heights resulting in what AFP described as one of the worst incidents of violence there since the 1974 truce accord. The IDF said troops "fired selectively" towards "hundreds of Syrian rioters" injuring an unspecified number in response to them crossing onto the Israeli side. According to the BBC, the 2011 Nakba Day demonstrations were given impetus by the Arab Spring. During the 2012 commemoration, thousands of Palestinian demonstrators protested in cities and towns across the West Bank and Gaza Strip. Protesters threw stones at Israeli soldiers guarding checkpoints in East Jerusalem who then fired rubber bullets and tear gas in response. In 2021, Nakba Day occurred during the 2021 Israel–Palestine crisis and at least 29 Palestinians were injured by Israeli security forces in the West Bank according to Al Jazeera English.

Shlomo Avineri has criticised observance of Nakba Day on the grounds that a more important issue is the failure to solidify a stronger national movement for Palestinian citizens as a foundation for nation-building. Arab citizens of Israel have also been admonished for observing Nakba Day in light of their higher standard of living when compared to that of Palestinians who reside outside of Israel.

On 23 March 2011, the Knesset approved, by a vote of 37 to 25, a change to the budget, giving the Israeli finance minister the discretion to reduce government funding to any non-governmental organization (NGO) that commemorates the Palestinian Nakba instead of the Israeli Day of Independence. A previous form of the bill, which first came under consideration by the Knesset in July 2001 and again in 2006, established the commemoration of the Nakba Day as a criminal offense, subject to 1-year imprisonment and/or a fine of NIS10,000 (~$2,500). Palestinians argue that the bill imposes restrictions on freedom of speech and expression, curtails equality, and applies conditions that suppress the national consciousness and historical narrative of the Palestinian people.

After months of legislative limbo due to numerous appeals filed by organizations such as Adalah and the Association for Civil Rights in Israel, as well as several Jewish and Arab citizens of Israel, the Supreme Court of Israel rejected the appeals, and upheld the Nakba Law, on 5 January 2012. Chief Justice Dorit Beinisch and Justices Eliezer Rivlin and Miriam Naor concluded: "The declarative level of the law does indeed raise difficult and complex questions. However, from the outset, the constitutionality of the law depends largely upon the interpretation given to the law's directives." Deductions could equal up to three times the event's sponsorship cost; repeat violations would double the amount of the fine.

• Al-Quds Day
• Day to Mark the Departure and Expulsion of Jews from the Arab Countries and Iran
• Farha (film)
• Naksa Day
• Ongoing Nakba

• What Palestinians protest every May 15: The Palestinian Catastrophe, explained. Vox.
• In pictures: 'Catastrophe Day' protests, BBC News
• nakba – Daily news and struggles from the Palestinian territory, Nakba news