Lahti (Swedish: Lahtis) is a city in Finland and the regional center of Päijät-Häme, located on the southern shore of Lake Vesijärvi in Päijät-Häme.

Lahti is the eighth largest city in Finland and the sixth largest urban area. Lahti has 120,078 inhabitants (30 June 2019) and covers an area of 517.64 km², of which 459.50 km² of land and the remaining 58.14 km² of inland waters (1 January 2020). Lahti is the youngest of Finland's so-called old cities.

On 1 January 2016, the City of Lahti and the Municipality of Nastola merged to form the new City of Lahti. The neighboring municipalities of Lahti are Asikkala, Heinola, Hollola, Iitti and Orimattila.


Lahti is located on the southern shore of Lake Vesijärvi, which belongs to the Kymijoki watershed. The first Latch Back passes through the city. The headwaters of the Porvoonjoki River are on the southern slopes of Salpausselä, and the upper reaches of the river run through the southern parts of the city. The town is characterized by the hillyness of Salpausselä and numerous lakes. Vesijärvi forms a gateway to central Finland via Päijänne.

Häme dialects are spoken in Lahti.

Lahti's strengths include environmental expertise and industrial design in particular.