A stock symbol or ticker symbol is a short abbreviation used to uniquely identify publicly traded shares of a particular stock on a particular stock market. A stock symbol may consist of letters, numbers or a combination of both. "Ticker symbol" refers to the symbols that were printed on the ticker tape of a ticker tape machine.

In the United States, modern letter-only ticker symbols were developed by Standard & Poor's (S&P) to bring a national standard to investing. Previously, a single company could have many different ticker symbols as they varied between the dozens of individual stock markets. The term ticker refers to the noise made by the ticker tape machines once widely used by stock exchanges.

The S&P system was later standardized by the securities industry and modified as years passed. Stock symbols for preferred stock have not been standardized.

Formerly, a glance at a U.S. stock symbol and its appended codes would allow an investor to determine where a stock trades; however in July 2007, the SEC approved a rule change allowing companies moving from the New York Stock Exchange to the Nasdaq to retain their three letter symbols; DirecTV was one of the first companies to make this move. When first implemented, the rule change did not apply to companies with one or two letter symbols, but subsequently any stock was able to move from the NYSE to the Nasdaq without changing its symbol. CA, Inc., which trades under the symbol CA, moved from the NYSE to the Nasdaq in April 2008 and kept its two-letter symbol.