OMX Helsinki 25 (OMXH25, formerly HEX25) is a stock market index for Helsinki Stock Exchange. It is a market value weighted index that consists of the 25 most-traded stock classes. The maximum weight for a single stock is limited to 10%. This is mainly to limit Nokia's weight in the index, although Fortum and Sampo Group were also capped in the February 2009 reshuffle.

As of the semi-annual review effective 1 August 2011, the following 25 companies make up the index:

The Helsinki Stock Exchange (Finnish: Helsingin Pörssi, Swedish: Helsingforsbörsen) is a stock exchange located in Helsinki, Finland. Since 3 September 2003 it has been part of OMX, referred to as OMX Helsinki (OMXH). Since NASDAQ's acquisition of OMX in February 2008, the official name of the Helsinki exchange has been NASDAQ OMX Helsinki.

The Helsinki Stock Exchange saw its first transaction on October 7, 1912. From then it remained a "free form" financial association until in 1984 it was converted into a cooperative owned mostly by banks, traders, other companies and associations.

On April 1, 1990, trading was moved to a new digital system: HETI (Helsinki Stock Exchange Automated Trading and Information System, and in Finnish a rough backronym for "immediately"), which replaced the electro-mechanical trading board originally introduced back in 1935. HETI enabled remote traders to do transactions on equal terms with those in the trading room.

The cooperative changed to a limited liability company (Helsingin Arvopaperipörssi) in the fall of 1995 and merged with several clearing and stock deposit companies and associations at the beginning of 1997. During 1997 and 1998 the Stock Exchange bought both of the Finnish derivative exchanges and merged them with itself to become HEX. In November 1998 HEX merged with Arvopaperikeskus to form Helsinki Exchanges Group Plc, which then changed its name to HEX Plc in the spring of 2001. In 2001 and 2002 HEX acquired a majority share of the Tallinn Stock Exchange and the Riga Stock Exchange.

Helsinki ( listen (help·info); Swedish: Helsingfors,  listen (help·info)) is the capital and largest city in Finland. It is in the region of Uusimaa, located in southern Finland, on the shore of the Gulf of Finland, an arm of the Baltic Sea. The population of the city of Helsinki is 596,233 (31 January 2012), making it by far the most populous municipality in Finland. Helsinki is located some 400 kilometres (250 mi) east of Stockholm, Sweden, 300 kilometres (190 mi) west of St. Petersburg, Russia and 80 kilometres (50 mi) north of Tallinn, Estonia. Helsinki has close historical connections with these three cities.

The Helsinki Metropolitan Area includes the city of Helsinki and three other cities: Espoo and Vantaa, which immediately border Helsinki to the west and north, respectively; and Kauniainen, which is an enclave within the city of Espoo. The Helsinki metropolitan area is the world's northernmost urban area among those with a population of over one million people, and the city is the northernmost capital of a EU member state. Altogether 1.1 million people, approximately one in five Finns, live in the Helsinki Metropolitan Area.