Helsinki is the capital and most populous city in Finland. It is on the shore of the Gulf of Finland and is the seat of southern Finland's Uusimaa region. About 684,000 people live in the municipality, with 1.26 million in the capital region and 1.6 million in the metropolitan area. As the most populous urban area in Finland, it is the country's most significant centre for politics, education, finance, culture, and research. Helsinki is 80 kilometres (50 mi) north of Tallinn, Estonia, 400 kilometres (250 mi) east of Stockholm, Sweden, and 300 kilometres (190 mi) west of Saint Petersburg, Russia. Helsinki has significant historical connections with these three cities.

Together with the cities of Espoo, Vantaa and Kauniainen—and surrounding commuter towns, including the neighbouring municipality of Sipoo to the east—Helsinki forms a metropolitan area. This area is often considered Finland's only metropolis and is the world's northernmost metropolitan area with over one million inhabitants. Additionally, it is the northernmost capital of an EU member state. Helsinki is the third-largest municipality in the Nordic countries, after Stockholm and Oslo. Its urban area is the third-largest in the Nordic countries, after Stockholm and Copenhagen. Helsinki Airport, in the neighbouring city of Vantaa, serves the city with frequent flights to numerous destinations in Europe, North America, and Asia.

Helsinki is a bilingual municipality with Finnish and Swedish as its official languages. The population consists of 75% Finnish speakers, 5% Swedish speakers, and 20% speakers of other languages (which is well above the national average).

Helsinki hosted the 1952 Summer Olympics, the first CSCE/OSCE Summit in 1975, the first World Athletics Championships in 1983, the 52nd Eurovision Song Contest in 2007 and it was the 2012 World Design Capital.

Helsinki has one of the highest standards of urban living in the world. In 2011, the British magazine Monocle ranked Helsinki as the world's most liveable city in its livable cities index. In the Economist Intelligence Unit's 2016 livability survey, Helsinki ranked ninth out of 140 cities. In July 2021, the American magazine Time named Helsinki one of the world's greatest places, a city that "can grow into a burgeoning cultural nest in the future" and is already known as an environmental pioneer. In an international Cities of Choice survey conducted in 2021 by the Boston Consulting Group and the BCG Henderson Institute, Helsinki was ranked the third-best city in the world to live in, with London and New York City coming in first and second. In the Condé Nast Traveler magazine's 2023 Readers' Choice Awards, Helsinki was ranked the 4th-friendliest city in Europe. Helsinki, along with Rovaniemi in Lapland, is also one of Finland's most important tourist cities. Due to the large number of sea passengers, Helsinki is classified as a major port city, and in 2017 it was rated the world's busiest passenger port.