Cat Ba is an island in the Cat Ba Archipelago of Vietnam's Ha Long Bay. Cat Ba is the largest island in the Bay and approximately half of its area is covered by a national park, which is home to the highly endangered Cat Ba langur.

The golden-headed Cat Ba langur is rarely seen, as fewer than 100 specimens are thought to survive in the wild, although it is the subject of a well-organized conservation program. The park covers both land and marine areas and has high biodiversity, although it is at risk from too rapid an increase in tourism. Other mammals in the park include civet cats and oriental giant squirrels.

Although there is much beauty to explore on the island, Cat Ba town itself is rather crummy: construction, massage parlours, blaring music, touts and drunk tourists. Cat Ba town is essentially a Vietnamese resort town (think Blackpool or Torremolinos) with large numbers of Vietnamese families coming to swim and relax on some of the nearest beaches to Hanoi as well as to take budget tour boats into Lan Ha Bay. 

- Wikivoyage