Kymenlaakso (literally Kymi Valley) (Swedish: Kymmenedalen) 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 Kymijoki. 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 55,000 inhabitants is located at the delta of River Kymijoki and has the most important import harbour in Finland. Other cities are Kouvola further in the inland which has after a municipal merger 88,000 inhabitants and the old bastion town Hamina.
Kymenlaakso was one of the first industrialized 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 deindustrialization, unemployment and population decline in Kymenlaakso, especially in those communes that were built around plants such as Myllykoski in Kouvola.