The companies that comprise the Dow Jones 30 Industrial Average are among some of the largest capitlization companies in the world. It is the index that most people think of as "The Stock Market". It is though not representative of the broader market as a whole.
The Standard and Poors 500, the Wilshire Index, or the Russell 2000 are more representative of the broader marekt. In terms of number of stocks that comprise them and the breadth of coverage they encompass in the various industries and sectors of business.
None the less the Dow 30 remains the psychological caretaker of the U.S. markets. The stocks in its average are massively large corporations that are well known to most people in the investing world. In terms of liquidity it is easy to buy and sell the stocks of these companies and execute a trade in a matter of seconds in today's online trading platforms. Many people remember when the Dow hit 10,000 for the first time or in the 2008 downturn when it fell under that number.
It is easy to find information on these companies, particularly since they are publicly traded. If you can gauge the sentiment of the market then you are halfway to making money in it.
Like all indexes they change components to it from time to time. They always take the weakest stocks and replace them with issues that represent the new generation of investor interest. Once the share price drops below a threshold and stays there for a length of time it is then delisted and replaced. General Motors was one such company that happened to in recent history.
