Trading

A stock exchange is an organization that provides a marketplace for either physical or virtual trading shares, bonds and warrants and other financial products where investors (represented by stock brokers) may buy and sell shares of a wide range of companies. A company will usually list its shares by meeting and maintaining the listing requirements of a particular stock exchange. In the United States, through the inter-market quotation system, stocks listed on one exchange can also be bought or sold on several other exchanges, including relatively new so-called ECNs (Electronic Communication Networks like Archipelago or Instinet).

In the USA stocks used to be broadly grouped into NYSE-listed and NASDAQ-listed stocks. Until a few years ago there was a law that NYSE listed stocks were not allowed to be listed on the NASDAQ or vice versa.

Many large non-U.S companies choose to list on a U.S. exchange as well as an exchange in their home country in order to broaden their investor base. These companies have then to ship a certain amount of shares to a bank in the US (a certain percentage of their principal) and put it in the safe of the bank. Then the bank where they deposited the shares can issue a certain amount of so-called American Depositary Shares, short ADS (singular). If someone buys now a certain amount of ADSs the bank where the shares are deposited issues an American Depository Receipt (ADR) for the buyer of the ADSs.

Likewise, many large U.S. companies list themselves at foreign exchanges to raise capital abroad.