Fibonacci Day is observed worldwide every November 23 to celebrate the contributions of the renowned Italian mathematician Fibonacci, also known as Leonardo Bonacci. The date is significant as it corresponds to the first four digits of the Fibonacci sequence when written in the mm/dd format (11/23). Fibonacci, born circa 1170 in Pisa, introduced the Hindu-Arabic numeral system to Europe through his book Liber Abaci, published in 1202, which also included the Fibonacci sequence. This sequence, where each number is the sum of the two preceding ones, has numerous applications in mathematics, computer algorithms, and various fields. Celebrations often include learning about Fibonacci's life and work, sharing facts on social media with the hashtag #FibonacciDay, and exploring the presence of the Fibonacci sequence and the golden ratio in nature, art, and architecture. Creative activities such as making art featuring the Fibonacci spiral or baking Fibonacci spiral cookies are also popular ways to commemorate the day.