Yom HaZikaron and Yom HaAtzmaut
Israel's Memorial Day and Independence Day — observed back-to-back on the 4th and 5th of Iyar.
Summary. Yom HaZikaron (Israel's Memorial Day, 4 Iyar) and Yom HaAtzmaut (Israel's Independence Day, 5 Iyar) are observed on consecutive days, a deliberate juxtaposition: grief immediately giving way to celebration, mourning rolling into joy, in graphic representation of the cost of statehood. Yom HaZikaron commemorates Israel's fallen soldiers and victims of terror; Yom HaAtzmaut celebrates the establishment of the State of Israel on 5 Iyar 5708 / 14 May 1948. The Chief Rabbinate of Israel established a special liturgy for Yom HaAtzmaut, including the recitation of Hallel (the praise Psalms reserved for major festivals).
Yom HaZikaron
The 4th of Iyar (or, when the date conflicts with Shabbat, adjusted to avoid). Sirens sound at 8:00 PM (the start of the day) for one minute, and again at 11:00 AM the next morning for two minutes; the entire country comes to a standstill. Ceremonies are held at every military cemetery in Israel; family members gather. Television and radio play memorial programming. The transition to Yom HaAtzmaut occurs in the evening; the shift from mourning to celebration is intentional and abrupt.
Yom HaAtzmaut
The 5th of Iyar marks the date of David Ben-Gurion's declaration of Israeli independence on 14 May 1948. The Chief Rabbinate's special liturgy includes: Hallel (with or without a blessing — a halachic dispute), the Haftarah of Yeshayahu 10:32–12:6, an additional 'Al Hanissim' insertion, and the recitation of the prayer for the State of Israel. The day is celebrated with barbecues (mangals), parades, public concerts, and family gatherings. Aerial displays by the Israeli Air Force are a Yom HaAtzmaut tradition; the President's Award for Outstanding Citizens is given on Yom HaAtzmaut eve.
The Halachic Question
Whether Yom HaAtzmaut warrants liturgical celebration is a contested halachic question. The Religious Zionist movement and the Modern Orthodox world generally answer yes — establishing a Jewish state in the Land of Israel after nearly two millennia is a manifestly miraculous event meriting a thanksgiving. Most Haredi authorities answer no — without a Sanhedrin, without the rebuilding of the Temple, the state is not yet the messianic redemption and does not warrant liturgical innovation. The middle position — affirming the religious significance of the state but not adopting full festival liturgy — is held by some. The Chief Rabbinate's liturgy is followed by most Modern Orthodox and Conservative congregations; many Haredi communities do not recite Hallel; most Reform congregations celebrate Yom HaAtzmaut with creative services.
Diaspora Observance
Diaspora communities observe both days, with Conservative and Reform congregations particularly active in Yom HaAtzmaut celebration. Israeli expatriate communities and Jewish federations organize public celebrations — flag-raising ceremonies, public concerts, falafel and shawarma events. The proximity of Yom HaZikaron and Yom HaAtzmaut, even in the diaspora, is observed deliberately — the joy is informed by the cost.
Where Denominations Diverge
Modern Orthodox, Religious Zionist, Conservative, Reform, Reconstructionist: all observe Yom HaAtzmaut with liturgical celebration. Haredi observance is mixed; the Satmar and certain other anti-Zionist communities do not observe at all. Yom HaZikaron is observed essentially universally in Israel as a civic day; in the diaspora, observance is most active in Modern Orthodox and Religious Zionist circles.
Sources
Israeli Knesset Law on Yom HaZikaron and Yom HaAtzmaut.
Chief Rabbinate of Israel, liturgy for Yom HaAtzmaut (1949).
Megillat Ha'Atzma'ut (the Israeli Declaration of Independence).
Further Reading
Daniel Gordis, Israel: A Concise History of a Nation Reborn.
Yitz Greenberg, The Jewish Way — modern observances chapters.
Rabbi Abraham Isaac Kook, Orot.