Kymenlaakso (Finnish: [ˈkymenˌlɑːkso]; Swedish: Kymmenedalen; lit. "Kymi/Kymmene Valley") is a region in Finland. It borders the regions of Uusimaa, Päijät-Häme, South Savo and South Karelia and Russia (Leningrad Oblast). Its name means literally The Valley of River Kymi. Kymijoki is one of the biggest rivers in Finland with a drainage basin with 11% of the area of Finland. The city of Kotka with 51,000 inhabitants is located at the delta of River Kymi and has the most important import harbour in Finland. Other cities are Kouvola further in the inland which has after a municipal merger 81,000 inhabitants and the old bastion town Hamina.

Kymenlaakso was one of the first industrialised regions of Finland. It became the most important region for paper and pulp industry in Finland. Since the late 1900s many plants have closed, which has caused some deindustrialisation, unemployment and population decline in Kymenlaakso, especially in those communities that were built around plants in Kouvola.

For history, geography and culture see: Uusimaa, Karelia and Tavastia

The region of Kymenlaakso consists of two sub-regions and six municipalities, three of which have city status (marked in bold).

Kotka-Hamina sub-region

Kouvola sub-region

For parliamentary elections, Kymenlaakso, together with the regions of South Karelia and South Savo, is part of the Southeast Finland constituency. The constituency elects 15 of the 200 members of the Parliament of Finland.