A stock market, equity market or share market is the aggregation of buyers and sellers (a loose network of economic transactions, not a physical facility or discrete entity) of stocks (also called shares), which represent ownership claims on businesses; these may include securities listed on a public stock exchange, as well as stock that is only traded privately.
In the middle of the 13th century, Venetian bankers began to trade in government securities. In 1351 the Venetian government outlawed spreading rumors intended to lower the price of government funds. Bankers in Pisa, Verona, Genoa and Florence also began trading in government securities during the 14th century. This was only possible because these were independent city-states not ruled by a duke but a council of influential citizens. Italian companies were also the first to issue shares. Companies in England and the Low Countries followed in the 16th century. Around this time, a joint stock company--one whose stock is owned jointly by the shareholders--emerged and became important for colonization of what Europeans called the "New World."
In 12th-century France, the courretiers de change were concerned with managing and regulating the debts of agricultural communities on behalf of the banks. Because these men also traded with debts, they could be called the first brokers. A common misbelief is that, in late 13th-century Bruges, commodity traders gathered inside the house of a man called Van der Beurze, and in 1409 they became the "Brugse Beurse", institutionalizing what had been, until then, an informal meeting, but actually, the family Van der Beurze had a building in Antwerp where those gatherings occurred; the Van der Beurze had Antwerp, as most of the merchants of that period, as their primary place for trading. The idea quickly spread around Flanders and neighboring countries and "Beurzen" soon opened in Ghent and Rotterdam.
By the end of October, stock markets in Hong Kong had fallen 45.5%, Australia 41.8%, Spain 31%, the United Kingdom 26.4%, the United States 22.68%, and Canada 22.5%. Black Monday itself was the largest one-day percentage decline in stock market history – the Dow Jones fell by 22.6% in a day. The names "Black Monday" and "Black Tuesday" are also used for October 28–29, 1929, which followed Terrible Thursday—the starting day of the stock market crash in 1929.
One of the most famous stock market crashes started October 24, 1929, on Black Thursday. The Dow Jones Industrial Average lost 50% during this stock market crash. It was the beginning of the Great Depression. Another famous crash took place on October 19, 1987 – Black Monday. The crash began in Hong Kong and quickly spread around the world.
The Paris Bourse, now part of Euronext, is an order-driven, electronic stock exchange. It was automated in the late 1980s. Prior to the 1980s, it consisted of an open outcry exchange. Stockbrokers met on the trading floor of the Palais Brongniart. In 1986, the CATS trading system was introduced, and the order matching process was fully automated.
According to one interpretation of the efficient-market hypothesis (EMH), only changes in fundamental factors, such as the outlook for margins, profits or dividends, ought to affect share prices beyond the short term, where random 'noise' in the system may prevail. The 'hard' efficient-market hypothesis does not explain the cause of events such as the crash in 1987, when the Dow Jones Industrial Average plummeted 22.6 percent—the largest-ever one-day fall in the United States.
The crash in 1987 raised some puzzles – main news and events did not predict the catastrophe and visible reasons for the collapse were not identified. This event raised questions about many important assumptions of modern economics, namely, the theory of rational human conduct, the theory of market equilibrium and the efficient-market hypothesis. For some time after the crash, trading in stock exchanges worldwide was halted, since the exchange computers did not perform well owing to enormous quantity of trades being received at one time. This halt in trading allowed the Federal Reserve System and central banks of other countries to take measures to control the spreading of worldwide financial crisis. In the United States the SEC introduced several new measures of control into the stock market in an attempt to prevent a re-occurrence of the events of Black Monday.
The total value of equity-backed securities in the United States rose over 600% in the 25 years between 1989 and 2012 as market capitalization expanded from $2,790 billion to $18,668 billion. Direct ownership of stock by individuals rose slightly from 17.8% in 1992 to 17.9% in 2007, with the median value of these holdings rising from $14,778 to $17,000. Indirect participation in the form of retirement accounts rose from 39.3% in 1992 to 52.6% in 2007, with the median value of these accounts more than doubling from $22,000 to $45,000 in that time. Rydqvist, Spizman, and Strebulaev attribute the differential growth in direct and indirect holdings to differences in the way each are taxed in the United States. Investments in pension funds and 401ks, the two most common vehicles of indirect participation, are taxed only when funds are withdrawn from the accounts. Conversely, the money used to directly purchase stock is subject to taxation as are any dividends or capital gains they generate for the holder. In this way the current tax code incentivizes individuals to invest indirectly.
Global issuance of equity and equity-related instruments totaled $505 billion in 2004, a 29.8% increase over the $389 billion raised in 2003. Initial public offerings (IPOs) by US issuers increased 221% with 233 offerings that raised $45 billion, and IPOs in Europe, Middle East and Africa (EMEA) increased by 333%, from $9 billion to $39 billion.
Rates of participation and the value of holdings differs significantly across strata of income. In the bottom quintile of income, 5.5% of households directly own stock and 10.7% hold stocks indirectly in the form of retirement accounts. The top decile of income has a direct participation rate of 47.5% and an indirect participation rate in the form of retirement accounts of 89.6%. The median value of directly owned stock in the bottom quintile of income is $4,000 and is $78,600 in the top decile of income as of 2007. The median value of indirectly held stock in the form of retirement accounts for the same two groups in the same year is $6,300 and $214,800 respectively. Since the Great Recession of 2008 households in the bottom half of the income distribution have lessened their participation rate both directly and indirectly from 53.2% in 2007 to 48.8% in 2013, while over the same time period households in the top decile of the income distribution slightly increased participation 91.7% to 92.1%. The mean value of direct and indirect holdings at the bottom half of the income distribution moved slightly downward from $53,800 in 2007 to $53,600 in 2013. In the top decile, mean value of all holdings fell from $982,000 to $969,300 in the same time. The mean value of all stock holdings across the entire income distribution is valued at $269,900 as of 2013.
Since the early 1990s, many of the largest exchanges have adopted electronic 'matching engines' to bring together buyers and sellers, replacing the open outcry system. Electronic trading now accounts for the majority of trading in many developed countries. Computer systems were upgraded in the stock exchanges to handle larger trading volumes in a more accurate and controlled manner. The SEC modified the margin requirements in an attempt to lower the volatility of common stocks, stock options and the futures market. The New York Stock Exchange and the Chicago Mercantile Exchange introduced the concept of a circuit breaker. The circuit breaker halts trading if the Dow declines a prescribed number of points for a prescribed amount of time. In February 2012, the Investment Industry Regulatory Organization of Canada (IIROC) introduced single-stock circuit breakers.
As of 2017, the size of the world stock market (total market capitalization) was about US$79.225 trillion. By country, the largest market was the United States (about 34%), followed by Japan (about 6%) and the United Kingdom (about 6%). These numbers increased in 2013.