A stock represents ownership. When you buy one share of a company's stock, you own a small fraction of that company — its assets, its earnings, its future. If the company does well, your share becomes more valuable. If it does poorly, your share loses value. That relationship between ownership and performance is the core logic of the stock market.
Companies issue stock to raise money. Rather than borrowing from a bank, they sell pieces of themselves to the public. The initial sale — an Initial Public Offering, or IPO — raises capital that the company can use to grow. After that, the shares trade between investors on exchanges, and the company itself is not directly involved in those transactions.
What Exchanges Actually Are
A stock exchange is a marketplace where buyers and sellers meet to trade shares. The New York Stock Exchange and Nasdaq are the most prominent in the United States. Most actual trading no longer happens on a physical floor — it's electronic, with orders matched by computers in milliseconds.
The price of a stock at any moment is simply what someone was willing to pay for it most recently. That price is determined by supply and demand. When more people want to buy a stock than sell it, the price rises. When more want to sell than buy, it falls. Those shifts in supply and demand are driven by expectations about the company's future earnings, broader economic conditions, news events, interest rates, and the collective psychology of millions of investors.
Why Stock Prices Move
Stock prices represent expectations about the future, not just the present. A company can be profitable today and still see its stock fall if investors believe future profits will be lower. A company can be losing money and still see its stock rise if investors believe it will be highly profitable eventually.
This forward-looking nature is why the stock market often seems to move contrary to the headlines. When the economy is in recession and unemployment is high, the stock market sometimes rallies — because investors are anticipating the recovery that hasn't happened yet. When the economy is strong and unemployment is low, the market sometimes falls — because investors are pricing in the expectation that interest rates will rise to control inflation, making corporate borrowing more expensive.
Indexes: The Summary Statistics
When news reports say "the market was up today," they're usually referring to an index — a number that represents the aggregate performance of a defined set of stocks. The Dow Jones Industrial Average tracks 30 large American companies. The S&P 500 tracks 500 large companies. The Nasdaq Composite is weighted toward technology companies.
These indexes are useful summaries but imperfect ones. A few very large companies have an outsized effect on the S&P 500 because the index is weighted by market capitalization — a company worth ten times as much has ten times the influence on the index. When people say "the market," they usually mean large American companies, which is not the same as the entire economy.
Bonds, the Other Half
The stock market often gets most of the attention, but the bond market is larger and equally important. Bonds are loans. When a company or government issues a bond, they're borrowing money from investors and promising to pay it back with interest. The interest rate on a bond reflects the perceived riskiness of the borrower.
Bonds and stocks tend to move in opposite directions during periods of stress — investors sell stocks and move into bonds as a safer alternative. This relationship is why a balanced portfolio typically holds both.
Why It Matters Beyond Investments
The stock market affects the broader economy in ways that extend beyond individual investors. When stock prices fall sharply, consumer confidence often falls too, reducing spending. Companies find it harder and more expensive to raise capital. Pension funds and retirement accounts shrink, which can reduce spending by retirees. The market is both a reflection of economic expectations and a factor that influences the economy it's reflecting.