Goa area and Sikkim are the only places in India where you can legally play casino games. The first casinos in Goa opened in the late 1990s in the hotels to the tourists, mainly with slots. First floating casino, Casino de Goa- Caravela opened on January 2001.
There are two types of casinos in Goa:Land-based casinos (onshore) and floating casinos on ships casinos (offshore) along along the Mandovi River and around Panaji.
Some of the offshore casinos also have onshore facilities.
Gambling in India was forbidden by religious issues. Goa ( most people is catholic -portuguese heritage) is a special and very touristic region . Gambling was allowed to attract tourists.
Offshore casinos were established as the Indian laws did not allow gambling on Indian land, but there was no regulation for offshore activities.
Why gambling in Sikkim?

Sikkim is a state in northeastern India. It borders China in the north and northeast, Bhutan in the east, Nepal in the west, and West Bengal in the south. Sikkim is the least populous and second smallest among the Indian states. Sikkim's capital and largest city is Gangtok.
The opening of several casinos in neighboring Nepal has led to a large number of Indians crossing the borders to play in these countries, leading to capital flight from India.
To combat this movement, the Government authorized the opening of casinos in Sikkim.First casino opened on 2009.

Reprodution of casinos and chips from CHIPGUIDE