Frankfurt (Oder), also known as Frankfurt an der Oder (German: [ˈfʁaŋkfʊʁt ʔan deːɐ̯ ˈʔoːdɐ]; Central Marchian: Frankfort an de Oder; lit. Frankfurt on the Oder) is the fourth-largest city in the German state of Brandenburg after Potsdam, Cottbus and Brandenburg an der Havel. With around 58,000 inhabitants, it is the largest German city on the Oder River, and one of the easternmost cities in Germany. Frankfurt sits on the western bank of the Oder, opposite the Polish town of Słubice, which was a part of Frankfurt until 1945, and called Dammvorstadt until then. The city is located about 80 kilometres (50 mi) east of Berlin, in the south of the historical region Lubusz Land. Within Frankfurt's city limits lies the recreational area Lake Helenesee.

The Oder is a river in Central Europe. It is Poland's second-longest river in total length and third-longest within its borders after the Vistula and Warta. The Oder rises in the Czech Republic and flows 742 kilometres (461 mi) through western Poland, later forming 187 kilometres (116 mi) of the border between Poland and Germany as part of the Oder–Neisse line. The river ultimately flows into the Szczecin Lagoon north of Szczecin and then into three branches that empty into the Bay of Pomerania of the Baltic Sea.