A list of companies used to measure how a market is performing. The FTSE 100 and S&P 500 are examples.
Market Index
A list of companies used to measure how a market is performing. The FTSE 100 and S&P 500 are examples.
By Scrimpr
Updated 18 Jan 2026 What is a market index?
An index is a list of companies grouped together to represent a market or sector. The index tracks how those companies are performing overall.
What are some examples?
The FTSE 100 is the 100 largest companies on the London Stock Exchange. The S&P 500 is the 500 largest companies in the US. The FTSE All-World covers thousands of companies across the globe.
When the news says “the market is up”, they usually mean an index like these.
Why do market indexes matter for investing?
An index fund copies an index. Instead of someone picking which companies to invest in, the fund just buys everything in the index.
This keeps costs low and means your investment matches the market rather than trying to beat it.
Key points about market indexes
- A list of companies grouped to represent a market
- Used to measure performance. How the market is doing
- Index funds copy them. Buy everything in the list
