Päijänne Tavastia or, officially, Päijät-Häme (Finnish: Päijät-Häme; Swedish: Päijänne-Tavastland) is a region in Southern Finland south of the lake Päijänne. It borders the regions of Uusimaa, Tavastia Proper (Kanta-Häme), Pirkanmaa, Central Finland, South Savo and Kymenlaakso. The biggest city in the region is Lahti.

Uusimaa (Finnish: [ˈuːsimɑː]; Swedish: Nyland, Finland Swedish: [ˈnyːlɑnd], Sweden Swedish: [ˈny̌ːland]; both lit. "new land") is a region of Finland. It borders the regions of Southwest Finland, Tavastia Proper (Kanta-Häme), Päijänne Tavastia (Päijät-Häme), and Kymenlaakso. Finland's capital and largest city, Helsinki, along with the surrounding Greater Helsinki area, are both contained in the region, which makes Uusimaa Finland's most populous region. The population of Uusimaa is 1,638,469.

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 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 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.