The Yom Kippur War, Ramadan War or October War (Hebrew: מלחמת יום הכיפורים‎ Milẖemet Yom HaKipurim or מלחמת יום כיפור Milẖemet Yom Kipur; Arabic: حرب أكتوبر‎ ḥarb ʾUktōbar or حرب تشرين ḥarb Tišrīn), also known as the 1973 Arab–Israeli War and the Fourth Arab–Israeli War, was fought from October 6 to 25, 1973, between Israel and a coalition of Arab states led by Egypt and Syria. The war began when the coalition launched a joint surprise attack on Israel on Yom Kippur, the holiest day in Judaism, which happened to occur that year during the Muslim holy month of Ramadan. Egyptian and Syrian forces crossed ceasefire lines to enter the Israeli-held Sinai Peninsula and Golan Heights respectively, which had been captured and occupied since the 1967 Six-Day War. Both the United States and the Soviet Union initiated massive resupply efforts to their respective allies during the war, and this led to a near-confrontation between the two nuclear superpowers.

Yom Kippur (Hebrew: יוֹם כִּפּוּר‎‎, IPA: [ˈjom kiˈpuʁ], or יום הכיפורים), also known as Day of Atonement, is the holiest and most solemn day of the year for the Jews. Its central themes are atonement and repentance. Jews traditionally observe this holy day with a 25-hour period of fasting and intensive prayer, often spending most of the day in synagogue services. Yom Kippur completes the annual period known in Judaism as the High Holy Days or Yamim Nora'im ("Days of Awe").

Yom Kippur is the tenth day of the month of Tishrei. According to Jewish tradition, God inscribes each person's fate for the coming year into a book, the Book of Life, on Rosh Hashanah, and waits until Yom Kippur to "seal" the verdict. During the Days of Awe, a Jew tries to amend his or her behavior and seek forgiveness for wrongs done against God (bein adam leMakom) and against other human beings (bein adam lechavero). The evening and day of Yom Kippur are set aside for public and private petitions and confessions of guilt (Vidui). At the end of Yom Kippur, one considers oneself absolved by God.