Assumption Day, also known as the Feast of the Assumption of the Virgin Mary, is a significant religious holiday observed in the Principality of Monaco. This Christian feast day is celebrated annually on 15th August. The day commemorates and honors the belief in the bodily ascension of the Virgin Mary into Heaven, as per the teachings of the Roman Catholic Church. As such, it is a day of immense religious importance to the predominantly Catholic population of the principality.

On Assumption Day in Monaco, devout Catholics attend a special church service at the beautiful Cathédrale de Monaco, which is the Princely family's parish church. People visit the church to offer prayers and participate in the Mass which is specially held in honor of the Assumption of the Virgin Mary. The day is also marked by various community activities, including processions and other public events. The religious occasion is a blend of solemnity and joyous celebrations.

Aside from the religious observations, Assumption Day is also a public holiday in Monaco, meaning offices, schools, and businesses remain closed for the day. The streets of Monaco are often lively with parades and festive activities, making it a great day for both locals and tourists. The day presents a good opportunity to experience the strong cultural heritage and religious traditions of Monaco. Undoubtedly, Assumption Day is one of the most important dates on the Monegasque calendar, reflecting both the religious devotion and the vibrant spirit of the people in this tiny, yet highly prestigious nation.