The Nikkei 225 (日経平均株価, Nikkei heikin kabuka^?, 日経225), more commonly called the Nikkei, the Nikkei index, or the Nikkei Stock Average (/ˈnɪkeɪ/, /ˈniːkeɪ/, or /nɪˈkeɪ/), is a stock market index for the Tokyo Stock Exchange (TSE). It has been calculated daily by the Nihon Keizai Shimbun (Nikkei) newspaper since 1950. It is a price-weighted average (the unit is yen), and the components are reviewed once a year. Currently, the Nikkei is the most widely quoted average of Japanese equities, similar to the Dow Jones Industrial Average. In fact, it was known as the "Nikkei Dow Jones Stock Average" from 1975 to 1985.

The Nikkei 225 began to be calculated on September 7, 1950, retroactively calculated back to May 16, 1949. Since January 2010 the index is updated every 15 seconds during trading sessions.

The Nikkei 225 Futures, introduced at Singapore Exchange (SGX) in 1986, the Osaka Securities Exchange (OSE) in 1988, Chicago Mercantile Exchange (CME) in 1990, is now an internationally recognized futures index.