메모리얼 데이(Memorial Day)는 미국의 공휴일로, 매년 5월의 마지막 월요일이다. 원래 미국 남북 전쟁 당시에 사망한 군인들을 기리기 위해 제정되었으나 제1차 세계 대전 이후로 전쟁 등의 군사 작전에서 사망한 모든 사람을 기리는 것으로 바꾸었다. 5월 마지막 주라는 계절적 특징과 겹쳐져, 최근에는 흔히 메모리얼 데이를 미국에서 여름 휴가철이 시작되는 기준으로 여기는 사람들이 많다.

Memorial Day (or Decoration Day) is a federal holiday in the United States for remembering and honoring persons who have died while serving in the United States Armed Forces. The holiday, which is currently observed every year on the last Monday of May, was most recently held on May 28, 2018. Memorial Day was previously observed on May 30 from 1868 to 1970.

Memorial Day is considered the unofficial start of the summer vacation season in the United States, while Labor Daymarks its end on the first Monday of September. In Canada, Victoria Day is a public holiday observed on a Monday one week before Memorial Day and similarly indicates the start of summer.

Many people visit cemeteries and memorials on Memorial Day, particularly to honor those who died in military service. Many volunteers place an American flag on each grave in national cemeteries.

Two other days celebrate those who serve or have served in the U.S. military: Veterans Day, which celebrates the service of all U.S. military veterans; and Armed Forces Day, a minor U.S. remembrance celebrated earlier in May, specifically honoring those currently serving in the U.S. military.