Malaysia Day is celebrated on 16 September every year to commemorate the establishment of the federation of Malaysia on the same date in 1963. 16 September 1963 is the most historical moment that shows the unification of the Federation of Malaya with Sabah, Sarawak, and Singapore (separated from Malaysia in 1965) to form Malaysia.

The formation of this new federation was planned to take place on June 1, 1963 but was later postponed to August 31, 1963 to allow it to be celebrated together with the 6th Independence Day celebration.

 Several issues related to the objections of Indonesia and the Philippines to the formation of Malaysia delayed the declaration until September 16 of the same year. The postponement was also made to allow the United Nations to allocate time for a referendum in North Borneo (now Sabah) and Sarawak.

 Malaysia Day is a public holiday in the state of Sabah in conjunction with the birthday of the Yang Di-Pertua Negeri. Although initially Malaysia Day was not a public holiday in Sarawak and Peninsular Malaysia, since 2010, Malaysia Day is also a public holiday in all states in Malaysia.