标普100指数是由标准普尔公司在标普500当中最强的100只成份股编写而成。
标普100指数是一百种范围广泛的工业股的，资本加权的指数。其构成股根据它们未成交的股份之总的市场价值而加权。每一发行股票的总的市场价值是每股的价格乘以未成交的股份数，每一构成股的价格变动，其影响同其总的市场价值成正比。所有一百种股票的这些因素加在一起，再除以一个事先决定的基准价值 (base value)。标普100指数的基准是根据由合并，收买，认股权，替代等原因而产生的资本化的变化而调整的。
据Apple Insider报道，由于原标普100公司、生物科技公司MedImmune被药厂阿斯利康收购，苹果实时成为标准普尔100指数成份股。
S&P 100 Index Trading Defined and Explained
As the name implies, the S&P 100 consists of 100 companies from a wide range of industries. The index is a sub-set of the S&P 500. The Standard & Poor's 100 Index is usually considered the benchmark for U.S. equity performance and liquidity. The S&P 100 is not just a list of the largest 100 companies. It is an index of 100 of the most widely held U.S.-based common stocks, chosen by the S&P Index Committee for market size, liquidity, and sector representation. According to the Index Committee, "Leading companies in leading industries" is the guiding principal for S&P 100 inclusion. While widely traded international companies are included, the Index Committee recently announced that only U.S.-based companies will be added in the future.
