The US market functions as reliably as it does partly because of the diversity of participants constantly active within it.

Retail investors are individuals buying and selling for their own accounts. Retail participation grew dramatically after platforms like Charles Schwab and Fidelity moved to zero-commission trading in 2019. Retail investors now account for roughly 20 to 25% of daily trading volume in the US.

Institutional investors are the largest force in the market. Mutual funds, pension funds, insurance companies, endowments, and sovereign wealth funds. They manage enormous sums and their decisions can move stock prices. They hold the majority of the value in US equity markets.

Market makers are the firms that stand ready to buy and sell continuously, providing the liquidity that makes instant execution possible. Without market makers, you would have to wait for a matching counterparty rather than transact immediately.

Hedge funds are pooled investment vehicles that use a wide range of strategies. They play a significant role in price discovery, the process by which new information gets reflected quickly in stock prices.

High-frequency traders use powerful computers to execute enormous numbers of trades in fractions of a second. They account for a significant share of daily trading volume. Their role is debated. But the basic effect of their activity is to keep prices tightly aligned across different venues and execution systems.

Brokers and broker-dealers are the intermediaries you interact with when you place an order.

Each of these participants has different objectives and different time horizons. Their constant interaction is what produces the continuous, efficient pricing that makes US markets function.