Lisbon is situated at 38°42' north, 9°5' west, making it the westernmost capital in mainland Europe. It is located in the west of the country, on the Atlantic Ocean coast at the point where the river Tagus flows into the Atlantic Ocean.

The city occupies an area of 84.8 km2 (33 sq mi). The city boundaries, unlike those of most major cities, are narrowly defined around the historical city perimeter. This gave rise to the existence of several administratively defined cities around Lisbon, such as Amadora, Queluz, Agualva-Cacém, Odivelas, Loures, Sacavém, Almada, Barreiro, Seixal and Oeiras, which are in fact part of the metropolitan perimeter of Lisbon.

The western side of the city is mainly occupied by the Monsanto Forest Park, one of the largest urban parks in Europe with an area close to 10 km2 (4 sq mi).