There are many different indexes in which you may invest. You may invest in a mutual fund or an exchange traded fund that mimics the performance of the index. The DJIA is an index of thirty top blue chip companies covering many segments in our economy. The index includes representative companies from various sectors of the economy, such as financial services, computers, and retail companies. The specific group of thirty stocks does not include sectors such as transportation or utilities, as they may be given special attention under another index. The index itself is not weighted by market capitalization, and it represents a good snapshot of how “the market” is doing at that moment.