BSE, the Bombay Stock Exchange, is one of India's two main stock exchanges, founded in 1875 on Dalal Street in Mumbai. It publishes the Sensex, an index of 30 large companies. Thousands of companies are listed on BSE, including many that are not on NSE, though most trading volume in India happens on NSE. A single company such as SBI can be listed on both exchanges, and its price is nearly identical on each because arbitrage keeps them aligned. When you place an order, your broker lets you choose the exchange, and for delivery investing it rarely matters. For derivatives, NSE dominates, while BSE has built its own index options market on Sensex and Bankex. Both exchanges are regulated by SEBI. Knowing which exchange you traded on matters mainly for reading your contract note and for the exchange transaction charges applied.