The Sundarbans is the largest single block of tidal halophytic mangrove forest in the world. The Sunderbans is a UNESCO World Heritage Site covering parts of India and Bangladesh.

The Sundarbans National Park is a National Park, Tiger Reserve, and a Biosphere Reserve located in the Sundarbans delta in the Indian state of West Bengal. Sundarbans South, East and West are three protected forests in Bangladesh. This region is densely covered by mangrove forests, and is one of the largest reserves for the Bengal tiger.

The name Sundarban can be literally translated as “beautiful forest” in the Bengali language (Shundor, “beautiful” and bon, “forest”). The name may have been derived from the Sundari trees that are found in Sundarbans in large numbers. Alternatively, it has been proposed that the name is a corruption of SamudrabanChandra-bandhe (name of a primitive tribe). However, the generally accepted view is the one associated withSundari trees

The Sundarban forest lies in the vast delta on the Bay of Bengal formed by the super confluence of the Padma, Brahmaputra and Meghna rivers across southern Bangladesh. The seasonally flooded Sundarbans freshwater swamp forests lie inland from the mangrove forests on the coastal fringe. The forest covers 10,000 km². of which about 6,000 are in Bangladesh. It became inscribed as a UNESCO world heritage site in 1997. The Sundarbans is estimated to be about 4,110 km², of which about 1,700 km² is occupied by waterbodies in the forms of river, canals and creeks of width varying from a few meters to several kilometers.

The Sundarbans Mangroves ecoregion on the coast forms the seaward fringe of the delta and is the world’s largest mangrove ecosystem, with 20,400 square kilometers (7,900 sq mi) of area covered. The dominant mangrove species Heritiera fomes is locally known as sundri or sundari. Mangrove forests are not home to a great variety of plants. They have a thick canopy, and the undergrowth is mostly seedlings of the mangrove trees. Besides the sundari, other species that make up the forest include Avicennia spp., Xylocarpus mekongensis, Xylocarpus granatum, Sonneratia apetala, Bruguiera gymnorrhiza, Cereops decandra,Aegiceras corniculatum, Rhizophora mucronata, and Nypa fruticans palms

A total 245 genera and 334 plant species were recorded by David Prain in 1903. While most of the mangroves in other parts of the world are characterized by members of the Rhizophoraceae, Avicenneaceae or Laganculariaceae, the mangroves of Bangladesh are dominated by the Sterculiaceae and Euphorbiaceae. Dominant flora includes:

The Sundarbans flora is characterized by the abundance of sundari, gewa, goran  and keora all of which occur occur prominently throughout the area. The characteristic tree of the forest is the sundari, from which the name of the forest had probably been derived. It yields a hard wood, used for building houses and making boats, furniture and other things. New forest accretions are often conspicuously dominated by keora and tidal forests. It is an indicator species for newly accreted mudbanks and is an important species for wildlife, especially spotted deer. There is abundance of dhundul or passur  and kankra though distribution is discontinuous. Among palms, Poresia coaractata and Myriostachya wightiana, and among grasses spear grass), khagra and golpata are well distributed.

The varieties of the forests that exist in Sunderbans include mangrove scrub, littoral forest, saltwater mixed forest, brackish water mixed forest and swamp forest. Besides the forest, there are extensive areas of brackish water and freshwater marshes, intertidal mudflats, sandflats, sand dunes with typical dune vegetation, open grassland on sandy soils and raised areas supporting a variety of terrestrial shrubs and trees.

The Sundarbans provides a unique ecosystem and a rich wildlife habitat. According to the 2011 tiger census, the Sundarbans have about 270 tigers. Although previous rough estimates had suggested much higher figures close to 300, the 2011 census provided the first ever scientific estimate of tigers from the area. Tiger attacks are frequent in the Sundarbans. Between 100 and 250 people are killed per year.

There is much more wildlife here than just the endangered Royal Bengal Tiger. Most importantly, mangroves are a transition from the marine to freshwater and terrestrial systems, and provide critical habitat for numerous species of small fish, crabs, shrimps and other crustaceans that adapt to feed and shelter, and reproduce among the tangled mass of roots, known as pneumatophores, which grow upward from the anaerobic mud to get the supply of oxygen. Fishing Cats, Macaques, wild boars, Common Grey Mongooses, Foxes, Jungle Cats, Flying Foxes, Pangolins, and spotted deer are also found in abundance in the Sundarbans.

The endangered species that live within the Sundarbans and extinct species that used to be include the Royal Bengal Tigers, Estuarine Crocodile, Northern river terrapins (Batagur baska), Olive Ridley Turtles, Gangetic dolphin, Ground Turtles, Hawks Bill Turtles and King Crabs (Horse shoe). Some species such as hog deer, water buffalos, Barasingha or swamp deer ,Javan rhinoceros, single horned rhinoceros and the mugger crocodiles or marsh crocodiles started to become extinct in the Sundarbans towards the middle of the 20th century, due to extensive poaching and man hunting by the British. There are several other threatened mammal species, such as the capped langurs ,smooth-coated otters .Oriental small-clawed otters and great Bengal Civets.

The forest also has immense protective and productive functions. Constituting 51% of the total reserved forest estate of Bangladesh, it contributes about 41% of total forest revenue and accounts for about 45% of all timber and fuel wood output of the country (FAO 1995). A number of industries (e.g. newsprint mill, match factory, hardboard, boat building, furniture making) are based on the raw materials obtained from the Sundarbans ecosystem. Various non-timber forest products and plantations help generate considerable employment and income generation opportunities for at least half a million poor coastal population. It also provides natural protection to life and properties of the coastal population in the cyclone prone Bangladesh.