King Bhumibol Memorial Day is a national holiday in Thailand, commemorating the life and reign of the country's beloved monarch, King Bhumibol Adulyadej, widely known as Rama IX. Born on December 5, 1927, and having served his kingdom from 1946 until his passing in 2016, King Bhumibol was the world's longest-serving head of state at the time of his death. The memorial day, which is observed annually on October 13th, marks the day of his passing. King Bhumibol was integral to shaping modern Thailand, and his memory is highly revered in Thai society.

On King Bhumibol Memorial Day, various activities take place all across the country in remembrance of the late King. These activities can range from religious ceremonies, such as alms offering to monks and merit-making rituals, to cultural performances. Significant landmarks and major streets are adorned with marigolds, a flower associated with the late King, while portraits of him can be seen in homes, businesses, and public spaces. Many Thais choose to wear yellow, the color associated with Bhumibol’s birthday, as a mark of respect.

King Bhumibol Memorial Day not only commemorates the late King but also serves to remind Thais of his teachings and principles, which revolve around diligence, patience, and mercy for the betterment of the people. His emphasis on sustainable development and self-sufficiency has had lasting effects on Thailand's agricultural policies. Moreover, King Bhumibol’s exceptional devotion to his people during his reign has left a profound legacy that continues to influence the moral and socio-political landscape of modern Thailand.