-Being included and traded on a given exchange. Most exchanges have specific requirements which companies must meet in order to be listed and continue to stay listed.

Companies are frequently being added to a given exchange, such as the NASDAQ. And occasionally, companies that have not fulfilled all necessary listing requirements become de-listed for a period of time until they again meet the requirements. Generally, companies prefer to be listed on the major exchanges, such as the NYSE and NASDAQ, since they provide the greater liquidity and visibility for a company's stock.

Dual Listing

-A company's securities are listed on more than one exchange for the purpose of adding liquidity to the shares and allow investors greater choice in where they can trade their shares.   

Dual listing is not a widely used technique, although it is thought to improve the spread between the bids and ask prices, which helps investors obtain a better price for their security. Hewlett-Packard (HP), for example, is listed on both the NYSE and NASDAQ.

Delisting

-The removal of a listed security from the exchange on which it trades. Stock is removed from an exchange because the company, for which the stock is issued, whether voluntarily or involuntarily is not in compliance with the listing requirements of the exchange.  

The reasons for delisting include; violating regulations and/or failing to meet financial specifications set out by the stock exchange. Companies that are de-listed are not necessarily bankrupt, and may continue trading over the counter. 

In order for a stock to be traded on an exchange, the company that issues the stock must meet the listing requirements set out by the exchange. Listing requirements include minimum share prices, certain financial ratios, minimum sales levels, and so on. If listing requirements are not met by a company, the exchange that lists the company's stock will probably issue a warning of non-compliance to the company. If the company's failure to meet listing requirements continues, the exchange may de-list the company's stock.