FTSE SmallCap is an equity index that tracks the performance of small-cap companies listed on the London Stock Exchange. The index is part of the FTSE UK Index Series, which includes several indices designed to measure the performance of various segments of the UK stock market.

The FTSE SmallCap Index comprises approximately 250-300 companies that are ranked below the FTSE 350 Index in terms of market capitalization. These companies are considered to be at the lower end of the market cap spectrum and are often newer, less established firms with significant growth potential.

The index is weighted by market capitalization, meaning that companies with larger market caps will have a greater impact on the index's performance. The FTSE SmallCap Index is used as a benchmark for small-cap equity portfolios and is often used by investors to gain exposure to small-cap stocks in the UK market.

The constituents of the FTSE SmallCap Index are reviewed quarterly to ensure that the index remains representative of the small-cap segment of the UK stock market. Companies that no longer meet the eligibility criteria may be removed, while new companies that meet the criteria may be added.