Boac is a first-class municipality and capital of the province of Marinduque in the Philippines. According to the 2015 census, it has a population of 54,730 people.

Boac is home to most of the province's commercial businesses. Barangays San Miguel, Murallon, and Mercado are the town's business district where the public market, medium-rise buildings, sports arena and Boac Town Arena, now Moriones Arena are. Meanwhile, Barangay Isok is home to the town's education district. Marinduque National High School, St. Mary's College of Marinduque, Don Luis Hidalgo Memorial School, Barangay Day Care Centers, Boac North District Office and the Division of Marinduque DepED Office is in Barangay Isok. The Municipal Building Hall is at Brgy. Tampus, adjacent is the Marinduque Museum at Brgy. Malusak.

The Marinduque Provincial Capitol is in Barangay Santol near the Dr. Damian Reyes Memorial Hospital (formerly Marinduque Provincial Hospital) and Camp Maximo Abad.

The name Boac is derived from the Visayan word bu-ak, which means "divided". The town had been divided in two by a river running from the eastern hinterland to the western plains down to the sea. The two were the Northern and the Southern areas.

Other records says that Boac came from the word "bulwak", which characterizes the tide caused by the rapids of the Boac River to its mouth in Brgy. Lupac and to the banks around the riverside barrios.

The first "visita" was established in 1580 and it was called "Monserrat de Marinduque" (now Boac) with Fray Alonzo Banol as its minister.

In 1621, the Spanish Jesuit missionaries brought the three-foot Marian image to Boac. So began the people's devotion to the image of the Virgin Mary.

In the mid-17th century, a group of Muslims in the Philippines called the Moro people felt threatened by the actions of the ruling Spanish government. They challenged the government by launching attacks on coastal Christian towns. This resulted in a raid along the shores of Barangay Laylay, near the Boac River.

During the siege, the neighbourhood people fled in panic and took refuge in the fortress church of Boac, which is now called Immaculate Conception Cathedral. In the meantime, all able-bodied men defended the outer walls of the church fortress against the attacks. Many Christians were killed and, by the third day of violence, those alive began to run short on food. The capture of the fortress seemed imminent.

...
Wikipedia