The S&P/ASX 200 Index (INDEXASX: XJO) is Australia's benchmark share market index. Launched in April 2000, it comprises the largest 200 companies on the Australian Securities Exchange by float-adjusted market capitalisation. It is one of a number of indices published by S&P Dow Jones on Australian markets (called the S&P/ASX family of indices).
As with all indices, the ASX 200 is measured in points and tracks the combined movements of all 200 shares within the index. Quarterly balances are performed to ensure the shares included in the index meet its eligibility criteria. These rebalances take place in March, June, September and December.
The index is largely dominated by the Financials and Materials sectors. The Financials sector alone makes up almost a third of the index and includes the big four banks such as Commonwealth Bank of Australia (ASX: CBA). Materials is the second largest sector and includes companies such as BHP Group Ltd (ASX: BHP) and Fortescue Metals Group Limited (ASX: FMG).
Investing in the index is simple: investors can buy shares in any ASX 200-listed company through a broker, or buy into an exchange-traded fund (ETF), which tracks the index as a whole and is traded like a common share.