The BSE SENSEX, also called the BSE 30 or simply the SENSEX, is a free-float market capitalization-weighted stock market index of 30 well-established and financially sound companies listed on Bombay Stock Exchange. The 30 component companies which are some of the largest and most actively traded stocks, are representative of various industrial sectors of the Indian economy. Published since January 1, 1986, the SENSEX is regarded as the pulse of the domestic stock markets in India. The base value of the SENSEX is taken as 100 on April 1, 1979, and its base year as 1978-79. On 25 July, 2001 BSE launched DOLLEX-30, a dollar-linked version of SENSEX. As of 21 April 2011, the market capitalisation of SENSEX was about  29,733 billion (US$593 billion) (42.34% of market capitalization of BSE), while its free-float market capitalization was  15,690 billion (US$313 billion).

The Bombay Stock Exchange (BSE) regularly reviews and modifies its composition to be sure it reflects current market conditions. The index is calculated based on a free float capitalization method—a variation of the market capitalisation method. Instead of using a company's outstanding shares it uses its float, or shares that are readily available for trading. The free-float method, therefore, does not include restricted stocks, such as those held by promoters, government and strategic investors.

Ketan Parekh is a former stock broker from Mumbai, India, who was convicted in 2008, for involvement in the Indian stock market manipulation scam in late 1999-2001. Currently he has been debarred from trading in the Indian stock exchanges till 2017. He was trainee of Harshad Mehta.

Parekh is alleged to have been involved in circular trading throughout the time period and with a variety of companies, including Global Trust Bank and Madhavpura Mercantile Co-operative Bank.

Parekh's sole conviction, which carried a one year sentence, came as a result of a transaction he conducted involving a unit of Canara Bank in 1992.

Though Parekh is currently barred from stock trading, in 2009, the Securities and Exchange Board of India alleged a variety of companies and other actors were trading on behalf of Parekh; 26 entities were banned from trading as a result of that investigation.