Gasan is one of six (6) municipalities comprising the province of Marinduque in the Mimaropa Region. The town is politically subdivided into twenty-five (25) barangays, and is a part of the Lone Congressional District of Marinduque.

Gasan is the second oldest municipality in Marinduque, after Boac. The town covers under its jurisdiction three offshore islands named Tres Reyes (Three Kings), a protected marine sanctuary that offers perhaps the best diving spot in the province.

Unknown to many, this town is also considered the butterfly capital of the Philippines, contributing 85% of the country’s butterfly and pupa exports. More than three-fourths of the butterfly breeders nationwide are based in this town and neighboring villages. Butterfly farming started only recently but is fast becoming an international growth industry with estimates of P100 million worth of exports. Worldwide, the market is estimated at $100 million (USD).

Marinduque Airport, the island’s only airport, is located in Barangay Masiga of this town.