The Hang Seng Index (HSI) is a freefloat-adjusted market-capitalization-weighted stock-market index in Hong Kong. It is used to record and monitor daily changes of the largest companies of the Hong Kong stock market and is the main indicator of the overall market performance in Hong Kong. These 50 constituent companies represent about 58% of the capitalisation of the Hong Kong Stock Exchange.
HSI was started on November 24, 1969, and is currently compiled and maintained by Hang Seng Indexes Company Limited, which is a wholly owned subsidiary of Hang Seng Bank, one of the largest banks registered and listed in Hong Kong in terms of market capitalisation. It is responsible for compiling, publishing and managing the Hang Seng Index and a range of other stock indexes, such as Hang Seng China Enterprises Index, Hang Seng China AH Index Series, Hang Seng China H-Financials Index, Hang Seng Composite Index Series, Hang Seng China A Industry Top Index, Hang Seng Corporate Sustainability Index Series and Hang Seng Total Return Index Series. Hang Seng in turn, despite being a public company, is controlled by another listed international financial institution HSBC Holdings plc. Both HSBC Holdings and Hang Seng are constituents of the index.