Cat Ba Island is the largest of the 366 islands that comprises the Halong Bay archipelago in Northern Vietnam and the only one that hosts a substantial settlement. While the vast majority of Halong Bay's islands are uninhabited vertical rocks, Cat Ba has a few fishing villages, as well as a fast-growing town. Except for a few fertile pockets, the terrain is too rocky for serious agriculture. Hence most residents earn their living from the sea, while others cater to the tourist trade.

Roughly 13,000 inhabitants live on the island and 4,000 more live on floating fishing villages off the coast. The large majority of the population can be found in Cat Ba Town which is located at the southern tip of the Island and is the commercial center on the Island. Since 1997, Cat Ba Town has grown rapidly and has become a tourist hub for both the Island and greater Ha Long Bay. The fishing community at Cat Ba town has been transformed by travellers during the past decade as the island has become a summer favorite with domestic tourists and a year round option for backpackers and travellers with ample time to explore less visited parts.

Life has always been hard here and many Cat Ba residents joined the exodus of Vietnamese boat people in the 1970s and '80s. Although the island lost much of its fishing fleet this way, overseas Vietnamese have sent back large amounts of money to relatives on the island, fuelling the hotel boom of the past decade.

Almost half of Cat Ba Island’s 354 square km, and 90 square km of the adjacent waters were declared a national park in 1986 to protect the island's diverse eco-systems. These include subtropical evergreen forests on the hills, freshwater swamp forests at the base of the hills, coastal mangrove forests, small freshwater takes and coral reefs. Most of the coastline consists of rocky cliffs. but there are a few sandy beaches hidden away in small coves.

For all of its natural beauty, Cat Ba Island faces numerous environmental problems going forward. In recent years, increase in tourism, illegal hunting and poaching, overfishing, and water pollution in Ha Long Bay have threatened the ecological integrity and biodiversity of the island, reducing and fragmenting the natural habitat for Cat Ba's numerous species.