Recently, many people have asked me how to quickly understand the U.S. stock market. The key lies in grasping four core U.S. stock indices. Many think there is only one major market index in the U.S., but in reality, because there are so many publicly traded companies in the U.S., it’s impossible to represent all companies with a single index. That’s why these four major indices each serve their own purpose.

The oldest is the Dow Jones Industrial Average, which was created as early as 1896. At that time, the U.S. was still in the industrialization era, with only 12 companies. Now, it has expanded to 30 companies. Because it uses a price-weighted system, stocks like Apple, which had very high share prices back then, had to split before being included. The Dow actually represents the performance of traditional economy and blue-chip stocks, making it suitable for gauging economic stability.

Later, as more companies went public, the S&P 500 index was introduced. Today, these 500 stocks account for about 75% of the total U.S. stock market capitalization. This index covers major industries, from tech giants to consumer brands, and has strict selection criteria—only companies with stable profits are included. If you want to grasp the overall direction of the U.S. economy, the S&P 500 is more accurate than the Dow.

The Nasdaq Composite is different. It was launched in 1971 by the electronic stock exchange and is mainly composed of tech stocks. As the tech industry grew, this index became a global barometer for technology stocks. Interestingly, the Nasdaq’s movements are highly correlated with Taiwan’s stock market, and many short-term traders use it as a real-time indicator of market sentiment—big gains in Nasdaq suggest investors are willing to take risks, while sharp declines often signal capital withdrawal.

The fourth is the Philadelphia Semiconductor Index, established in 1993, tracking 30 representative semiconductor companies. With explosive demand for 3C products, cloud computing, and AI, the market value of semiconductor stocks has increased significantly. TSMC is also part of its components, making this index increasingly influential on Taiwan stocks.

An interesting phenomenon is that these four indices often move in different directions. For example, Nasdaq may fall while the Dow rises. This is essentially sector rotation—funds selling overperforming tech stocks and shifting into undervalued traditional or defensive stocks. This doesn’t mean the market is crashing; it just indicates a change in capital allocation. Therefore, investors shouldn’t only watch the indices’ overall rise or fall but also observe which sectors are leading—those are the directions where capital is flowing. When all four indices move in the same direction, the trend’s reliability increases.

Regarding how to invest in these U.S. stock indices, there are three methods. The first is ETFs, which are traded like stocks, with low management fees, but no leverage and only long positions. The second is futures, which have time limits and leverage, typically settled every three months. They can be used to go long or short, but because of leverage and the lack of daily price limits in U.S. stocks, the risks are higher—mistakes can lead to significant losses. The third is Contracts for Difference (CFD), similar to futures but without expiration dates, offering higher leverage and more suitable for short-term traders. CFDs also allow for lower margin investments.

In the long run, if you believe the U.S. economy will continue to grow, investing in U.S. stock indices is like riding the wave of rising tides. For example, the S&P 500, which includes the top 500 companies by market cap, has an automatic mechanism to weed out weaker companies and retain stronger ones. Investors don’t need to worry about whether their holdings have long-term competitiveness—just ensure the country’s economy keeps growing. This is also a strategy Warren Buffett highly advocates. For long-term investing, regularly buying ETFs with fixed amounts is recommended; for short-term profit, futures and CFDs are useful. Their ability to go long or short, combined with moderate leverage, makes them flexible tools for both hedging and speculation.