Calcutta Botanic Garden occupies a prime riverside site three miles downstream from the centre of Calcutta. It is most famous as the home of the world's largest tree, a vast spreading banyan. Its grand avenues, named after its founders and the fathers of Indian botany, convey something of its former glory. In the nineteenth century it was the greatest of all the colonial botanic gardens and an important scientific institution; two of its superintendents were knighted and one went on to become Director of the Royal Botanic Gardens at Kew, the very centre of the imperial botanical network. The Garden is of considerable importance as it was one of the earliest institutions in India based on western science. This survey will look at the reasons for its foundation, and how it successfully established itself in its first twenty years.