A tracker fund is an investment fund that invests the money of a large number of clients. It essentially tracks the movement of a group of stocks and shares (which is known as an index). When the index performs well, the tracker fund does as well. Likewise, if the index drops, the tracker fund will also drop in value, and the value of each client’s investment will fall. Each stock market has at least one index. In the UK, the FTSE 100 is an index that comprises the biggest 100 UK companies.