The Tokyo Stock Price Index, commonly known as the TOPIX, is an important stock market index for the Tokyo Stock Exchange in Japan, along with the Nikkei 225. The TOPIX tracks the entire market of domestic companies and covers most stocks in the Prime market and some stocks in the Standard market. It is calculated and published by the TSE. As of January 2025, there are planned to be 1,716 companies listed on the TSE, since about 400 stocks with low liquidity were phased out after the TSE reform in 2022. The index transitioned from a system where a company's weighting is based on the total number of shares outstanding to a weighting based on the number of shares available for trading. This transition started in October 2005 and was completed in June 2006. Although the change is a technicality, it had a significant effect on the weighting of many companies in the index, because many companies in Japan hold a significant number of shares of their business partners as a part of intricate business alliances, and such shares are no longer included in calculating the weight of companies in the index. Wikipedia