These 82 constituent companies represent about 58% of the capitalisation of the Hong Kong Stock Exchange.

[2] HSI was publicized 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.

Hang Seng in turn, despite being a public company, is controlled by another listed international financial institution HSBC Holdings plc.

[5] When the Hang Seng Index was first published, its base of 100 points was set equivalent to the stocks' total value as of the market close on July 31, 1964.

Its all-time low is 58.61 points, reached retroactively on August 31, 1967, after the base value was established but before the publication of the index.

On 24 June 2016, the market fell 1,000 points in response to UK EU referendum results that "Leave" won the vote against "Remain".

The full contract specifications are below: The following table shows the annual development of the Hang Seng Index, which was calculated from 1964.

[9][10] On January 2, 1985, four sub-indices were established in order to make the index clearer and to classify constituent stocks into four distinct sectors.

As of February 2024 they are:[11] The Hang Seng Composite Index Series (恒生綜合指數) was launched on October 3, 2001, targeting on providing a broad standard of the performance of the Hong Kong stock market.

ii) A company will be classified into different sectors according to its majority source of sales revenue(or profit or assets if relevant).

iii) Re-classification of a stock's Industry Sector will occur once the company's business has undergone a major change, such as, substantial merger or acquisition.

HSI constituent stocks are selected with the use of extensive analysis, together with external consultation.

To be qualified for selection, a company: Guidelines for Handling Large-cap Stocks Listed for Less than 24 Months For a newly listed large-cap stock, the minimum listing time required for inclusion in the stock universe for the HSI review is as follows: Among the eligible candidates, final selections are based on their: The current Hang Seng Index is calculated from this formula: