National Foundation Day (建国記念の日, Kenkoku Kinen no Hi) is a national holiday celebrating the mythological foundation of Japan on 11 February 660 BC.

The origin of this day starts on the New Year Day in the traditional lunisolar calendar when the foundation of Japan by the mythical Emperor Jimmu was celebrated, according to Nihon Shoki*. The year 660, however, is way earlier for any known emperor of Japan and there is no historical evidence for Emperor Jimmu.

The holiday was originally proclaimed in 1872, January 29 which corresponded with the Lunar New Year of 1873. Unexpectedly to the government, this lead to people seeing the day as just Lunar New Year and not the National Foundation Day which prompted the government to move the holiday to February 11 of the Gregorian calendar in 1873. The government stated it corresponded to Emperor Jimmu's regnal day, but no method of computation was published.

Originally, the holiday was named Kigensetsu (紀元節) and was considered one of the four major holidays in Japan. Celebrations included parades, athletic competitions, public reading of poems, singing of the national anthem and patriotic speeches. The celebration became the model for school ceremonies, though on a much smaller scale.

Still, it was not until later that everyone understood what Kigensetsu meant to celebrate, some believing it was Meiji Emperor's birthday. The confusion was caused, mostly in rural areas, by the fact that most peasant's kids did not attend school. By the 1890s all rural areas in Japan acquired a school and so in 1910 Kigensetsu finally started to be viewed as a holiday that united the whole Japanese nation.

Kigensetsu was abolished during WWII after the surrender of Japan and was reinstated as National Foundadtion Day in 1966. Although still a day for expressing patriotism, National Foundation Day did not hold any reference to the Emperor Jimmu.

Now, as a public holiday, although schools, banks and many companies are closed, there is no public celebration and no attention given by mass media to the holiday. Even expressions of patriotism in public are rare.

Nihon Shoki - is the second-oldest book of classical Japanese history. The book is also called the Nihongi (日本紀, "Japanese Chronicles")